I served in the RAF as a pilot for 22 years - mostly flying heavies, as it happens. I also spent 5 years involved in the selection of those who wished to join via University Air Squadrons. As the cut-and-paste from OAT's website suggests, you will be found out if your intention is to use the RAF as a stepping-stone to the airlines.
However, let's assume that you are fully committed to the idea of 16 years defending Queen and Country, flying whatever Her Majesty's Royal Air Force commands you to, in whatever dirty, dangerous and faraway little wars should come up in that time. At the end of those 16 years you can reasonaby expect to have 2000 to 3000 hours flying time in your Eurofighter Typhoon or whatever. You would probably have spent some time as an instructor, either in a Basic Flying Training School on Tucanos, or Advanced FTS in Hawks. You might well have spent some time as a weapons instructor in the Typhoon OCU, or on your squadron. You will also certainly have spent many months or even years away from home, living in basic accommodation, flying over some God-forsaken desert in support of yet another UK-US 'peace' operation. You also are likely to have spent one tour (three years or so) in a ground appointment of some kind.
You could, of course, be dead. I saw many, many mates' funerals in my 22 years.
Assuming you survive, at the end of those 16 years the RAF may offer you the chance to serve to 55, with, currently, some significant financial sweetners, or you may leave. On leaving, you would currently receive a tax-free lump sum of many thousands of pounds, and a pension. And a few exemptions from the ATPL requirements. Joining the airlines at that point would be entirely achievable and reasonable.
However, let's suppose that you decide after flying training that the RAF isn't for you. You will be, of course, released from the service - though the RAF I believe still does reserve the right to charge you for the training you received. I don't believe they've ever excercised this right, but the bill would be in millions of pounds! You'd leave with a couple hundred hours, no qualification, no money and a recently-acquired reputation for wasting people's time. Not good if you're now looking for a job!
Think very carefully about your next step.