I want to become a commercial pilot, can you do that through the RAF?
Yes, you can. It means giving a commitment for a fair number of years in service of your country, where you will be trained as a pilot (assuming you get on to that - there are more jobs in the RAF than just pilot!). After your service, one thing you can do with your military flying experience is become a commercial pilot.

When I was young enough to consider it, there were 3 ways to become a commercial pilot


Learn in the airforce
Pay your own way (PPL, CPL, ATPL etc)
Get a scholarship from a big carrier like BA. There were usually about 4-6 given per year to the highest achievers.