In their recent Capital Markets Plan BA announced that all the 737s would be retired by the end of 2014 and the charts show a total of 16 new "Airbus Family" joining from next year up to 2018. These are over and above the 7 currently on order for LHR but there was no detail to explain what they were or where they were going. I guess these 10 are part of that expansion with the remaining 6 replacing the outgoing short haul 767s at LHR (possibly A321s?).
As I understand it, there are 11 ex BMI A319s (G-DBCx) which are moving down to LGW as the new A320s are being delivered at LHR. Leasing a further 10 A320s will means a total of 21 airbus planes replacing 19 737s which suggests in addition to more capactity at LGW there will also be a few new routes launched (which is what was said in the Capital Markets Plan too).
All in all, good news for LGW travellers.