"David Tennant turned up to record an episode of Paul O’Grady’s chat show a couple of weeks back..."
What Tennant said was from a few weeks ago, last week is the most current news; they begin production in April
This is from the article you linked:
"Recently, Cary Elwes told us that this film was still set to go and that he would be before the motion capture cameras as of next Spring. Can we really trust Tennant’s information over that of one of the film’s announced stars? It certainly wouldn’t be the first time somebody one might assume to be near the centre of a production was running on out-of-date information.