Ford Fiesta [1995] M-Reg: Power Trouble?

To strip the problem to it's most basic form, the engine is repeatedly cutting out in lower gears. The problem first appeared a while back as I set off on a journey. I'd barely got into second when then engine just cut out. Afterwards I was unable to start the car either. It was turning over but not starting. However, when I returned to the car later, it started fine and I drove it back to it's normal parking space.

All seemed fine, but on a journey back home [60 mile journey], the engine once again just cut out right at the end of my journey as I waited at traffic lights. The power itself remains on, the radio, lights etc, but the engine simply stops. There's no noise or jerk to accompany it, it just stops.

A mechanic has looked at the car and believe the problem to be the injection. Apparantly the petrol wasn't being properly fed through to the engine. Even after having a new one fitted however the problem persists. The car will drive fine, and then simply refuses to start up, or cuts out in one of the lower gears. Generally the higher gears seem to avoid the problem.

Any help welcome.

Thanks.