Scroggs, I presume your use of the term 'o-level' is referring to GCSE?
Yes! Sorry - showing my age.
Pilot Pete is quite correct; having the DofE Gold on your CV may make a difference if you're very young with little experience other than school, university and your flying school. It's not a given however, as it will depend on the interviewer knowing about the scheme - there are many who don't.
The RAF is a quite separate consideration. Unlike the civilian world, you are not being employed as a pilot; you are being employed as an Officer, who will have many responsibilities and tasks quite unrelated to flying an aeroplane. You will be a manager, a dispenser of authority and discipline, required to instill respect in those you may be tasked with being responsible for. You will be groomed towards ever greater managerial and military responsibility and you will sometimes be expected to take posts which involve no flying whatsoever.
This requires quite different qualities from the airline business, which requires from you essentally nothing other than being the best you can be within the flight deck. BA and a very few others do ask, sometimes quite junior, pilots to take on managerial roles, but these very rarely require the individual to give up flying. In fact, those full-time managerial posts that require aircrew experience are usually filled by medically-grounded pilots. Most airlines will want nothing from you other than flying qualifications, a pleasant manner, and an ability to work when the rest of the world is asleep!
Scroggs