Edit update * thanks everyone for suggestions and help, I checked all earth cables and checked voltage on everything…. Then realised my alternator belt was missing 
Hi all, need some help on my Mk1 1.6 1992.
Was driving home last night, revs running high at about 2000, stopped at petrol station and it wouldn’t start back up. Lights were on really dim, managed to bump start it and get it home.
Battery is fine, alternator is only 2 years old, rev counter works but jumps all over the place which it has never done before. Has recently had the cam belt done about 4 months ago. Any ideas?
The alternator belt would have been taken off while replacing the cam belt. Check it is back on and tensioned correctly. Have you noticed any squeaking?
I’m assuming that it doesn’t crank over now. Have you checked the condition of the earth strap for the battery negative terminal to where it bolts to the body in the boot?
“Lights were really dim”. This is your clue. It can only mean that system voltage is low. It means one of the 3 things: A bad ground, a bad battery or a bad alternator. What is the actual voltage with the car running?
Battery is reading just under 13V with car turned off, can’t check with running unless I jump start it. Do you know where and how to check all the earth points?
That all looks fine, nope no squeaking at all