how do i fix my s reg ford fiesta?

evening all
my s reg ford fiesta has started playing up lately, last friday i pulled up in the car park at tesco then my car wouldnt start. we tried it saturday and sunday and no luck then monday after doing nothing to it it started. by tuesday it did same again wouldnt start. i got a mechnic to look at it and he couldnt find anything wrong with it. but it started working again then today 1 day later again its stopped working again. it seems there is no fuel going to the engine when it wont start. have i got a faulty fuel pump?
any ideas
cheers
adam