learning to fly? another approach entirely!
ac_ppl, I am somewhat surprised that nobody on this thread has suggested learning to fly properly....WITHOUT an engine! They are called gliders.
As you live near London, why not visit the London Gliding Club? near Dunstable,
or my club, near Banbury, called Shenington.
That way you get started on the basics. Effects of controls. Weather - very important! safety...looking out for other aircraft, etc etc.
And if you fail your medical, you are probably still OK to fly solo in a glider.....
I started in gliders, got the PPL later and did a lot of tug flying which somebody else pays for!
It won't hurt to get a bit of real flying in while waiting for your medical!
Happy landings!