The UK uses the FAA MMEL for SEP fixed wing aircraft and its a right ball ache to find on the web.
As for your problems with the stall warner I should imagine about 50% of the training cessna's in the UK suffer from what could be call stall warner failure.
Its not really failed its just old and crap linked with bent airframes gives a pathetic strangled honk if your lucky to get anything instead of a decent honk. If its a C170 it's maybe just not stalling. The one I used to fly didn't unless you g loaded by doing some that isn't taught in the PPL. For a level power off stall the ASI used to read zero there was no buffet no nose drop it just wafted down with full control back at about 600ft/min it was a bugger to land as well until you got the knack of dropping it.
And for the people who say you have to suck on the hooter before every flight you are welcome to getting half a kilo of midges in your mouth. And putting a hanky over the top does nothing to prevent coughing for the first half hour of the lesson be it student or instructor who gives it a suck. And even if it makes a noise on the ground experence has shown that doesn't mean it will work in the air.
If you tell us the type we can give a bit more help some types its a bit more vital they work eg PA38