According to Total Sci-Fi, ITV have decided to axe Primeval, citing budget concerns. An insider elaborated:
"Basically ITV have changed their policy about drama before 9pm in that they've decided they really don't want any, at least not of the quality and cost of Primeval. The show remained as popular this run (in terms of audience share) as ever before but the fact is that everyone knows ITV have money problems and they've decided that whatever drama budget they've got left is better spent after 9pm. It's a great shame as Primeval was bringing new viewers to ITV who will now only be served by the BBC, but there's nothing we can do about that."
"At the point where we finished the third series, we had every reason to believe we would be doing a fourth. Had we known there was any likelihood of cancellation, clearly we wouldn't have left half the cast marooned up a tree in the distant past. We can understand that some fans might be frustrated by this ending and we're sorry for that. It certainly wasn't our plan to leave things so uncertain. That said, some fans may know that there are ongoing talks for both a film and a North American series version of Primeval and if and when those projects come to fruition we will make every effort to carry on the story in a suitable way."
"Obviously we're devastated that things should end this way with ITV. But we're absolutely certain that although this stage of its evolution seems to be over, Primeval isn't dead. We're very proud of what we've achieved over the past three years and we have every intention of keeping Primeval alive in other ways."
I have to say, while I'm not exactly inconsolable over this news, it is unfortunate the show ended on a cliffhanger. And it's always a shame when British sci-fi takes a hit. The show is inexplicably very popular on BBC America. Still, I suspect the proposed US remake/spin-off and big-budget movie will probably improve on what was always a well-intentioned but exasperatingly dumb TV series.