Shelly asked a question about the differences between how British TV shows are written compared to American shows, primarily in terms of the production system that goes on behind-the-scenes. This is a common question I have occasionally half-answered in comments here, although I'm not really best placed to give true "insider knowledge". But, broadly speaking, here are the differences as I've come to perceive them:
In the US, most people understand that "showrunners" (sometimes one, often a duo, sometimes a trio or more) are paid to literally run the show. They hire writers to come "on staff" to help write the show they've created, usually 8-13 people. Generally, the entire show's storylines are discussed and individual episodes "broken" (brainstormed, plotted, debated, structured, etc) in the famous "Writer's Room", before writers are assigned to write specific episodes into workable drafts. Those drafts then go through a process of rewrites, often as a result of "notes" that the showrunners or network bosses give as feedback. Eventually, a script is locked and filmed. io9.com have a great article interviewing various American writers about the process, which is well worth checking out.
It's a very regimented, productive, creative way of making TV as part of a "team". It needs to be, because US TV has to produce many hours of scripted entertainment a year. A standard network show churns out 20-25 episodes of TV over a 12-month period -- although there does appear to be a shift towards doing less episodes these days, for a variety of reasons. One reason cited is that American viewers are starting to dislike having their viewing broken for hiatus (particularly mid-season in winter), and would prefer shows just run through with little interruption. This is perhaps because DVD box-sets have become very popular.
The UK system is less regimented and turnaround is slower, although there is still a professional process of course. The notion of a "showrunner" is less prevalent in the British industry (having only become popularized thanks to Russell T. Davies role as chief writer of Doctor Who), but there are obviously still executive producers who are in control of TV drama.
Still, there isn't really one established system for getting TV shows written in the UK. Many sitcoms are the work of 1-4 people, and the process is often like an author being asked by a publisher to deliver a novel. There are deadlines involved, sure, but it's still something of a "cottage industry". This author-like approach to sitcoms is generally why British comedies are more idiosyncratic than US counterparts (or feel purer creatively), because every script's the work of fewer people, whereas US sitcoms go through the aforementioned Writers' Room process like a sausage factory. Each system has its pro's and con's, so you could argue a preference all day. In my opinion, a good British sitcom burns bright but fast, while a good American sitcom has more longevity but tend to lose their spark and dwindle after 3 or 4 years. Generally.
With regard to soaps (a very popular drama format in the UK), there are people employed just to storyline continuously, and writers are like hired guns brought in to fashion a script around what's already been decided needs to happen. I'm sure they have input and certain freedoms, but given the fact UK soaps each air around 2-hours of TV per week, the system just demands that a core group decide on the plots and writers come in and make that plan a written reality. Some writers are permanent employees who are used to this system, others may only drop in for a few episodes, perhaps with the intention of regular work.
For drama, the system's similar to what US TV does (and increasingly so), but there are still big differences. The key thing is that UK TV can't afford to pay annual salaries for "staff writers" to be employed year-round and perhaps only write a few scripts themselves. The fact UK drama tend to only air 8-13 episodes a year means they can't justify the "machine" mentality of the US Writers' Room. And it doesn't really need it, to be honest. If UK production companies could afford to make 24 episodes a year, that would obviously have to change how they do things, but they don't so they won't.
What tends to happen is that the producers/showrunners write their show's premiere and finale, then perhaps a few episodes in-between, and effectively call on other writers to fill the gap under their stewardship. It's a bit like the soap system, but I liken it to journalism: an editor of a magazine needs help with a massive publication, so hires in some freelance scribes to help write some articles.
I don't know this for a fact, but it seems to me that big BBC shows like Merlin, Ashes To Ashes and Doctor Who follow that model. The "showrunner" is the "author" of the entire year's story, deciding the arcs of plot and character, while often thinking up every episode's core idea or thematic intention. But they can't write every episode themselves, so other writers are hired in. Just recently on Doctor Who, Mark Gatiss was told by Steven Moffat to write a story that involved (a) Winston Churchill, (b) World War II and (c) Daleks. The result was "Victory Of The Daleks", which I'm sure Moffat also polished and amended slightly (if only to add the series motif of the "glowing crack-in-time" at the very end), but it was basically Gatiss' script he created based on a brief by the showrunner. Moffat's predecessor, Russell T. Davies, would apparently rewrite all the scripts delivered to him quite extensively (with the exception of Moffat's, tellingly), but I'm not sure if that's something Moffat does, too. But if he does, then Doctor Who is still very much one man's vision, filtered through some trusted accomplices.
This UK system seems to work pretty well for drama, all things considered. But there are flaws from an audience perspective. The biggest problem is that there's less "meeting of minds" because there's no Writers' Room to focus imaginations and deliberate storylines. That means every series of UK TV drama is tangibly the work of one of two people and not a "think tank" of talent. Of course, while some people will say that "two minds is better than one, so imagine what could be done if TEN minds worked on a drama", you could also argue that "too many cooks spoil the broth" and the UK's lucky there's less interference with how drama's written.
Also, having a single showrunner pulling together their masterplan can be great, but if you personally don't like what they're doing you can be in for years of heartache because their style isn't something you respond to, and there's no hope of effecting change. The best example of that is Russell T. Davies' tenure on Doctor Who, which split opinion because some adored his style... while others hated it from the start, or grew bored by it. And now we may get years of Steven Moffat, although he seems to be more popular because most people agree he's a better writer with a more fertile imagination, but there are still those who dislike some of his creative choices (the multi-coloured, hunchbacked Daleks) and approach to character.
If there was a US-style Writers' Room working on Doctor Who, chances are Moffat may have been dissuaded from altering the Daleks -- who knows. But I think we can agree that the output of the UK process is more "concentrated", as there's no committee where a showrunner could have his/her opinion changed. Of course, I'm not suggesting that Moffat can literally do whatever he damn well pleases, because there are executive producers with clout who can overrule him, but as the chief writer he's certainly entrusted with the creative direction to a large extent. Hey, if the guy who's been a fan of Doctor Who all his life thinks Daleks need to resemble giant crayons now, he knows what he's talking about, right? I bet that's the thinking behind closed doors.
Anyway, Doctor Who's unique because it's by far the biggest ongoing project on British TV, and one that demands fulltime commitment from its production crew and the regular actors. That's why David Tennant needed a year's break, because the show is back-breaking work from a British perspective. It may only air 13 episodes and a Christmas special every 12-months, but that's the work of a much smaller production crew working on a tiny budget compared to their US counterparts. It's quite astonishing Doctor Who looks as good as it does, really. Chuck probably has twice the budget of a typical Who episode, and I know which ones looks cheaper to me.
The reason a few showrunners like Toby Whithouse (above, Being Human) and Howard Overman (Misfits) can find time to write for Doctor Who and Merlin, respectively, is that -- simply put -- the shows they run aren't such a massive undertaking. Being Human only lasts 8 episodes and Misifts was only 6 episodes long. Overman also seemed to be quite hands-off with Misfits once the scripts were delivered, if the DVD extra features are any indication (i.e. he was nowhere to be seen!) It feels like those guys are more creators/lead writers and not true "showrunners" in the Doctor Who sense.
I have no idea if Whithouse was always on-set for Being Human, but I don't think either show really demands their creators are. That's actually pretty normal, as even US dramas don't always need the showrunners involved in the filming process. On Lost, Damon Lindelof and Carlton Cuse were always in L.A writing and coordinating the creative backbone of the show, and were rarely onset in Hawaii. Obviously there were logistical issues on that show, but it goes to show that showrunners don't have to be standing behind a director's shoulder and rewriting scripts on location. They're involved with the editing, though.
So, given the easier shows they run, Whithouse and Overman can fill their spare time by writing for other shows. Hey, you want a vampire episode of Who set in Venice, Mr. Moffat. No problem! I have some time to kill before I need to sit down to write Being Human again.
To answer a few other questions Shelly had:
Q: What roles if any do UK showrunners play other than writing? Do they produce? Direct? Anything else?
A: By definition, showrunners produce and manage. It's possible they would direct episodes if they were qualified to, but that's very rare. Joe Ahearne (Ultraviolet, Apparitions) is the only person I can think of who wrote and directed the shows he created. Quite the auteur! But, generally speaking, showrunners tend to be producers/writers. I've heard stories of British creators/writers of a TV show being taken off set when they tried to change something, because they weren't considered important enough to stick their nose in! This is why a lot of British writers/creators also want to make sure they're a producer on their show these days... so they can't be frog-marched off sets! I think this is what happened with Peep Show's Sam Bain and Jesse Armstrong.
Q: Are the writers under contract once employed with a particular show and how much freedom do they have to work on something else?
A: I'm not sure. I would assume a showrunner is contracted for a certain period of time to work on a show, but I doubt that means they're not allowed to do other things when the show's not in production. There isn't the cash available to pay for a showrunner to sit around for four months of the year waiting to get started, much as they'd love that to be the case!
Q: Is scriptwriting taught in the UK film schools? Or how do they get their start?
A: Yes, there are no major differences between how the UK and US develop new writers, that I can see. There are screenwriting courses, film schools, people are self taught, the usual rigmarole of trying to get an agent, etc. If anything, the UK is more open to "unsolicited" spec scripts than the US system, though. You can send something to the BBC's Writers Room and it has to be read because the BBC's a service for license payers of the UK. Many independent production companies do likewise.
But it's still rare that a total novice will get a spec script made -- such is the volume of material submitted every year. And, unlike the US, the UK system just isn't large enough to accommodate the thousands of aspiring writers out there. Even the US has its limits. But, y'know, that's not to say there's no point trying, because obviously the system does have success stories. James Moran springs to mind: he was just a humble Sci-Fi Channel competition winner in the late-'90s, managed to get a movie script made (Severance) in the mid-'00s, and that led to him writing for Doctor Who, Torchwood and Spooks recently. Not a bad decade for him, right?