Just to let you know, this can be done without removing anything. Just done mine, it's taken me about 3 hours of messing about but eventually figured out how to do it (hopefully after reading this it'll be a bit quicker for you)!
1) Buy the springkit from Ford (comes with spring and random plastic spring which I didn't use) - costs about £4.
2) Have a look at someone elses focus (if your not sure where the spring locates).
3) Insert 1p pieces between every coil of the spring, on both sides (probably around 30 in all), this will "temporarily" stretch the spring enough so that you can just insert it into the required position.
4) Have a feel around at the top of the pedal for a small hole (you'll put the longer hook of the spring through here first).
5) Have a look with a torch at the metal plate behind the clutch pedal on the chassis for a small hole (you'll put the shorter hook of the spring in here).
6) Depress clutch pedal to gain some tension on the spring (some coins may drop out at this stage, otherwise, push/pull then out by hand.
Thanks for this advice it worked a treat. Took me less than an hour and a half. Used 28 pennies, the only thing I did different was attach the spring to the chassis first.