looking at the bulkhead from the front of the car, there is a small plastic box in the top left hand corner of the bulkhead, what is its purpose, and how do i remove it for inspection or replacement? its the one with a small diameter tube coming from it.

Can you give us a photo of the offending part?

not at the moment, its a box about 3 inches square and its sort of connected to the bulkhead and the top of the inner wing

If you mean this part-

It's the brake fluid reservoir.

Yeah you dont need to touch that mate

no its not, it is some kind of sensor inside a box i think

top left of picture, black box

Looks like some sort of vacume sensor again its not something ide tamper with or aware needs touched a great rule of thumb with a ford is if it aint broke dont touch it lol

Ah, I saw 2004 Focus in your profile and imagined a Mk2.

Let me cast an eye over my ole mk1 Haynes.

Evaporator canister purge valve.

It's part of the emissions control system.

There's one bolt as visible top right and another one under the bottom left corner.

Thanks for that

You're welcome.

just to clarify, this is the box i mean....