This DS article refers to an interview with Alexander Siddig (a new cast-member for Series 4) where he makes fleeting reference to Primeval, in the first page of that interview. At the end of the DS article, it is mentioned that:
The new [series] of Primeval will premiere in January on ITV1.
I may have missed something before, but I'm pretty sure that's the first real word on Series 4's premiere date. I mean, we shouldn't really set our hopes on that - remember last series? Plus, we don't know where this info is coming from. But, it is promising, that they're confident enough to put a month on the article.