Just had a mk2 focus in with this problem and Tony's description is spot on,there is one extra to do on an "ordinary" focus and that is the radiator has to be dropped down, hoses etc can be left in place,it is then possible to see the latch bolts and with a squeeze and a 1/4 drive ratchet it is possible to undo the bolts and release the latch.

The link piece that connects the latch to the cable drive is available as a seperate part, part no 4549268 and is £2.25.This whole set up is an anti-theft device in that if a screwdriver is used to force the lock,when the whole barrel rather than the lock mechanism is turned the cable moves backwards from the latch and disconnects the release cable.