Perhaps someone in the UK or a subscriber can confirm this (we won't see the issue on newsstands here in Canada for weeks yet), but apparently Steven Moffat announced in the newest Doctor Who Magazine (#418) that the new season will be called Season 31. I got this off the Wikia site for Doctor Who, so if someone who has the issue could confirm, that would be great!
This is after DWM previously reported that the BBC was planning to start the numbering over again with Series 1, and as recently as last month Moffat wrote in his DWM column that he favored "Series Fnarg".
Personally, I'm quite happy to see the long history of the series being honored. The whole idea of "Series 1" back in 2005 was to not scare away new viewers, but I think 5 years later people get the picture, and all that "is it part of the canon?" stuff should have been laid to rest the moment Sarah Jane met John Smith as well. Hopefully the BBC might do a bit of merchandising "retcon" and when Series 1-4 inevitably end up on Blu-Ray (upgrading The Next Doctor showed it is feasible) maybe they'll be rebranded Series 27-30.
Alex
This is after DWM previously reported that the BBC was planning to start the numbering over again with Series 1, and as recently as last month Moffat wrote in his DWM column that he favored "Series Fnarg".

Personally, I'm quite happy to see the long history of the series being honored. The whole idea of "Series 1" back in 2005 was to not scare away new viewers, but I think 5 years later people get the picture, and all that "is it part of the canon?" stuff should have been laid to rest the moment Sarah Jane met John Smith as well. Hopefully the BBC might do a bit of merchandising "retcon" and when Series 1-4 inevitably end up on Blu-Ray (upgrading The Next Doctor showed it is feasible) maybe they'll be rebranded Series 27-30.
Alex