engine prob

i have mk1 1.8 8v…. it can run for weeks some time months but then you will be drivin alone as normal and the engine just cuts out. then you have to wait 4 about 20 mins before it will start again… ????
any idears what could be the problem??

Immobiliser?
Ignition barrel
Distributor hall sender
damaged wire in engine bay
fuel pump relay
the list goes on but keep an eye on the rev counter when it next does it and see if it instantly drops which would indicate an electrical problem