Before i burn this heap, what on earth could be causing this issue?

2 litre blacktop zetec.

Its totally random, it will do it when its hot, when its cold whenever, but not everytime, probably 1 in 3 times of going to start it, where basically you will turn the key and it just spins over and either doesnt fire or its trying to fire.

Ignition off, back on again, start, it will spin over a couple of times, and fire up, idle really rough then its fine?

It had a full service 4000 miles ago, plugs, all filters, fluids, belts, timing is fine, everything is fine.

It refused to start about a month ago but never did it again, now it appears the problems come back and more often?