Having travelled frequently on those Caribbean services, I was surprised that a hot English breakfast was on offer on approach to LHR from SIN a month or so later.
I'm sure you must appreciate a 7 or so hour flight is going to be catered differently to a 13 + hour flight whether it is or not departing from or arriving into to LHR or LGW. This doesn't just apply to BA.
The majority of passengers would not want to be served a Full English breakfast meal just a few hours after eating a full 'evening meal' on an overnight flight from the Caribbean / North America.
BA's Longhaul onboard product offering from both LHR and LGW is pretty much the same. There are some minor differences due to different suppliers on some catering products i.e dessert pots / breakfast box styles...
As on shorthaul, there are different catering bandings on the longhaul flights too. These depend on flight length / destination / and sometimes can include competition...