You won't find any 1.4 focuses (foci?) on this side of the pond so all I can offer is some Focus generic advice.
First you need to describe your no start condition a bit better: Engine cranks but won't catch or engine won't crank at all? What's a short stop (time-wise?)
Secondly, don't assume that just because the car won't start that it's the starter motor. Electrical problems throughout the starting circuit can cause no start conditions. It's usually set up like this: Battery - fuse - ignition key switch - starter motor relay - starter motor solenoid - starter motor. Each component in the circuit needs to be verified as working. You also have the anti-theft system to worry about if you have a no crank condition.
Finally, the car needs to be in good working order before it'll start, obviously. Old plugs, dirty air filters, plugged fuel filters, vacuum leaks, etc. will all prevent a rapid and clean start.
a short stop is like when im getting petrol,i bought it 2nd hand & havent got the original imobiliser key,would that affect it?,it starts 1st time in the mornings or after a long stop,its just really frustrating!