wouldn't start, it will turn over but not start.

My citroen C3 (03 plate in case it matters) has been running perfectly for the last 6months (since I bought it second hand!) the other day I tried to start it but the car wouldn't start, it will turn over but not start. The AA came out and said it was a back flow problem with the injectors, has anyone had this fault and if so is it an expensive fix?
Some one else mentioned I might be starting it before the glowplugs have warmed up but I don't seem to have a glowplug indicator! is it there and I'm missing it?
The AA did get my car started by leaving their foot on the accelerator while the car is turning over until it started which is what I'm doing now but I'm worried that I'm damaging the car or making the fault worse.
Any advice greatly appriciated

Hi Jo81

Disregard this bit:

Some one else mentioned I might be starting it before the glowplugs have warmed up but I don't seem to have a glowplug indicator! is it there and I'm missing it?

(03 plate in case it matters)

Yes, along with the engine size, confirmation of the fuel type, number of valves and the miles its covered.

Do you get any smoke out the exhaust, when you are starting, when its running?

It would be worth seeing if any codes have been logged, but this will need the car connecting to a computer for diagnosis.