I've had this exact problem with my (59) plate fiesta, It seems to be worse in colder weather i was wondering if anyone else had found that the squeak improves or goes away completely when the weather gets warmer.
If not i'd better get it looked at by ford, as i have tried greasing it and found it to only be a temporary fix.
It's a winter thing. Completely disappears in the summer.
I think it is a batch fault and is infuriating.