Now that you all talk more about stuck in advance, the cogs in my brain are moving and it kind of makes sense taking in account something else I noticed today - my idle is at about 1100rpm just with the return spring pulling it, if I want less I have to physically pull it back, say like putting my foot under the accelerator and pulling it up - and then looking at the carb, the idle adjusting screw is not even touching the cam...
So... are my cogs working in the right way thinking that if the auto advance is stuck, then the revs are higher, once I get it unstuck, revs drop down, then I can use the idle adjuster to get the revs right...and has nothing to do with the return spring being too weak. (this was something I was going to investigate next)
You reckon it should be alright to drive 1 mile down the road?
I would rather wait till after the MOT to start investigating this properly, just in case I mess something up tomorrow and get stuck (also only have about 1h free tomorrow to look at it)
If so I'd leave it till thursday and then report back on my findings - always like to close all my questions with the solution in case it helps someone else along