Just last week I passed my CPL so now have a fATPL and can fly for a living. It is indeed fairly hard to get a job in an airline, but it is getting easier at the moment due to less well qualified pilots around, meaning airlines have been slowly and reluctantly lowering their requirements. Easyjet for example, who I'll be working for when Ive done my type rating, were previously wanting pilots with 1500hours, but this has reduced to 'only'! 500hours, for certain positions though. I'll be entering having only around 250hours, as Im on a cadet course and am 'sponsored' by the airline. This of course may not be the case in 2-4 years or whenever you start to apply for jobs as its a pretty cyclical process. You certainly dont need to do into the RAF etc to build up your hours to get into commercial flying as someone said, thats just wrong.
You'll probabaly want, although not necessarily need for some jobs, A-levels in Maths and Physics, as these subjects form the basis of the ATPL exams or I expect something similar for the armed forces - you need and its helps if you can understand how the aircrafts flying and how its systems work.