ABS for AE86?

[Blue86]

I personally wouldn't bother.
It all depends on how you drive. I have been driving for 12 years, all my cars don't have ABS, live in Southland New Zealand, so we get heaps of rain, snow etc and have never needed it. I learnt to pulse brake when I was a kid on the farm in the ute doing skids in the paddock, which is the same as ABS.
We have a race AE86, ABS is definitely not a good thing in that, and you tend to use the throttle to get yourself out of trouble.

Biggest thing, don't do stupid shit on the roads and you won't need ABS.
and if you do, learn to drive out of your cock up with the throttle as apposed as the brake.

As far as the UK spec, I wouldn't have a clue. Need to talk to you local MOT (i think it's called that, here its WOF) inspector regarding changes needed to put on the road.