Paul wrote:
I have a pretty new Worcester Bosch Combi 27Cdi, and the plastic key
used to lock and unlock the link cannot be removed from the unlock
position. As it is plastic, and the fitting is plastic, I am reluctant
to apply to much force!! At the moment it is left in, just turned to
the unlocked position, and I don't suppose it will do any harm that
way, but how can it be removed please?

If it is in the unlocked position just pull it out. There is an O ring
seal that will resist but then it should pop out.