Non Starting 1997 R Fiesta 1.2?

This is a car with under 50k on the clock which periodically will not start. The battery is bang on but there is not even a click, just a whoosh from the choke working. I tried bumping it off but although the ignition appears to be on, nothing. In the past it has only done this for my wife and eventually gone back to normal. Not this time, any ideas?