Might I recommend reading through this - likely to remain much the same for future years but not, of course, guaranteed:
Future Pilot Programme - Future Pilot ? Other Information and FAQs
Most specifically:
The year 1 basic salary for a Future Pilot Programme first officer is £23,220, with a further £8-£10,000 of flying allowances typically being earned in a full year of flying (please note that these allowances are not guaranteed and are subject to levels and type of flying completed). Remember that as well as pay and allowances, British Airways will pay you back your security bond, tax–free, at the rate of £12,000 per year for the first seven years of your employment as a pilot.
It is worth bearing in mind that for some applicants this represents a substantial pay cut. This does not make them any less keen; competitive process this!
Edit: What my fellow Mancunian said!