Every time I release the footbrake there is a little squeak (moving parts needing lube type squeak).  I've had a poke around but can't work out where it's coming from - sounds like it's just behind the pedals.  Anyone have and clues what might be the culprit?

Something in the pedal box? Wont be accessible though will it?

in the old days, the rear drum brakes used to do this as the shoes slid against the back plate

Squirt it with WD40

I don't use WD40 when I can't see where it's going - it kills seals and isn't too good for electrical connections.  Is there a sealed box the other side of the footwell?  if so that could be where it's coming from...

You can use silicone based lubricant, completely inert.

In pedal box case I'd not be concerned about seals

In any case, strip it and see what is squeaking if not willing to go for a simple solution.

I'd personally squirt some WD40 and forget about it, not worth a hassle really...