My 2010 1.4 Fiesta Zetec behaved like it was running out of fuel a couple of days ago. The engine died down to a tick over. After a minute or so it picked up again and carried on as though nothing had happened. It has done this a couple of times since then, starts to die and then carry's on as normal. There is always plenty of fuel. Any suggestions ?

Could be a blockage in the fuel somewhere but would advise a obd scan first

Petrol or diesel?

Its a 1.4 Petrol. I understand that there is some type of valve in the fuel line that gives problems from time to time.

I'm not sure which valve you mean.  Purge valve perhaps?  

I would suspect a throttle position sensor issue with this particular engine myself.

The only valve in the fuel line I can think of would be the one that cuts it off if you have a crash; but that would close it off completely.  If you are certain that it is fuel-related, it might be a blocked fuel filter, or a failing pump.  Measuring the fuel pressure might help; but it might require you to disconnect fuel lines (I don't know if your model has a Schrader valve on the fuel rail - sadly, mine doesn't), and so can be slightly hazardous.  There are plenty of youtube videos for checking fuel pressure, but make sure you get a kit with the correct connectors for a Ford.