Its worth pointing out that you won't be considered a DEP unless you meet the criteria for one and apply via the DEP process. If you pay your own way through a CAP509 course (or whatever they are these days) BA consider you a self sponsored CEP, which means you get £2K more basic pay than a BA sponsored CEP but basically you're on the same reduced pay scales as a CEP. This is so that BA can recover the large sums of money they've invested in your ab-initio training, and nothing to do with them trying to rip you off.

Just another thought here. I know the question was about pay at BA but have you considered other airlines? It is highly unlikely you would get a job with BA straight off. Airlines like the holiday companies (Air 2000, Monarch, Britannia etc.), the low cost carriers and people like BMI start their FOs on around £38k+ On top of that you get your allowances, share options, and lots of other benefits. Also, time to command is alot shorter than at BA with most of these airlines, and you would then see your salary increase by a large amount. There is no bidlines at these companies and so everyone does their fair share and being junior doesn't mean you'll get all the crap flying.
Just a thought.

So why do people leave the aforementioned companies to join BA, and not vice versa. BA, the original, and still the best.

I would say that getting any job straight out of an approved course takes luck, time, perseverance, and the right contacts. But BA is still the no.1 choice for most people. They are also the largest employer of pilots in the UK, and in the end it usually comes down to numbers.

Harry