Many thanks, ***** ***** just going to ask if you could find something similar please give me a minute to look up the spec.
These models generally have a mechanism which is fixed by friction and a mechanical washer, which eases off by appling downward pressure as you turn the tap off (anti clock wise), then you pull upwards as you rotate anti clockwise.
Its a rather poor design, and looking at the age will probably need some playing but a reasonable amount of force will be needed.
Sorry John my mistake, you want to fully close the tap while apply downward force, and try lifting up once tap closed and rotating clockwise.
If this doesnt work it may simply be secured by friction, and worth trying to get some WD40 in the spindle and lever it off with a screw driver, if its still held on fast, use a blow lap and give it a lick to try and warm up and that should help free it for you.
So it wasnt a BB fixing after all, glad you freed the tap, I guess its one of those things it looked from the photo it was one piece.