Somebody mentioned Belavia moving from LGW. That could be a strong possibility as they sometimes use the Embraer 175.
With quite possibly 1.5 million extra passengers in 2014, Stansted should be back up to about 19 mppa (more than the 2010 levels).
Luton should definitely be well into 10 million by 2014 and is likely to be their best ever year so far. Quite a bit of an increase from Monarch and Wizz in particular as well as the couple of new operators they've had.
It's great to see both airports potentially doing extremely well next year. So far it's looking like Stansted and Luton could be the UK's fastest growing airports in 2014.