I think that it is mostly down to your training and flying background.
BA still seem to have a preference for those that have done integrated training (or at least trained at a one stop, established training school) - and this still seems to apply even with experience on type. The couple of guys from my outfit that weren't invited to interview were both from the modular route with elements of their training done abroad. Of course there will be exceptions to this but from my experience, if you've got FTE, CTC, Oxford, Cabair on your CV it's a good start.
Similarly, if you've been flying for a familiar UK (European??) airline it is likely to help. At the last round of recruitment it seemed to be mostly guys and gals from the UK loco's and charter operators with the odd middle east major thrown in. Obviously it's now opened up to non-type rated applicants so folk will be coming from different types of airlines, however I would have thought that BA will want to have some confidence that you come from an outfit with a well respected high standard of training.
Only after these 2 factors will they then start to look at other things such as essay answers. As someone has already stated, flying hours are pretty much irrelevant - as long as you have the minimum stated on the application requirements. Only my opinion of course!