I used to work at Gatwick and keep in touch with those that do. Here are some details:
Flying Hours: Max 800hrs April to March (but may rise soon!)
Leave: 4 weeks per year rising to 6 weeks after approx 18 months.
Days Off: 11 days per month in blocks of 1, 2, 3, 4 or even 5. There is no set pattern.
Rostering: Preference system called “Carmen”. You express a preference for the type of flying you would like to do. The more senior you are the more likely you are to get the work you ask for: but still no guarantee! The rosters for say April are issued in the middle of March. Roster stability is very good.
The type of work on offer:
1. Tours of 2 to 6 days away. Typically 3 or 4 sectors a day. Some include a day free of duty in the middle so you get to explore your destination. Mostly you will have minimum rest on a night stop (ie. 12 hours).
2. Day Trips: 2 or 4 sectors. The short two sector days generally have horrendous start times of 4 or 5am eg. Amsterdam and back. Some of the 4 sector days are very long eg. Pristina and back then Manchester and back. Some are very inefficient ie. you spend 12 hours at work and only do 5 hours flying.
3. Night Flights. Eg. Bucharest: landing at 6am back at Gatwick.
4. Reserve: A block of up to 6 days which could be anything from Airport Standby to a 5 day tour. You find out the night before.
So, you may bid for day trips and weekends off but get given 5 day tours and Tuesday and Wednesday off. The more junior you are the more likely your preference will be ignored.
In summary, if you get day trips you will work similar hours to the low cost operators but with no fixed roster pattern. The difference is that you can express a preference to do tours instead. The other benefit is that you join the BA Seniority list with the option to go Long Haul and, shortly before you retire, get a command!