The Wormhole wrote:
I thought double-banking was only done with seasons 2-4 because they had to accomodate Christmas specials. Since season 5 didn't need to do that (Christmas Carol would have been filmed with season 6) there wouldn't be any need for double-banking.
They didn't "fully" double-bank episodes until series 2, but it had also been done to an extent in series 1 with parts of "The Long Game" being filmed with Adam while "The Empty Child"/"The Doctor Dances" were still being filmed with the Doctor/Rose.
There wouldn't have been any double-banking in series 5 if everything went according to schedule. But the show had a brand new production team, who knew about the difficulties back in the first year. It would be reasonable for Moffat to have commissioned "double bankable" scripts with an eye to that being a possibility if the schedule ending up slipping as it had in years past.