Martin Underwood wrote:

Has the OP tried the various things that have been suggested? Did any of
them work? And the crucial question: did he manage to clean off the stain
before SWMBO noticed it?

Well, he tried turps (is that the same as white spirit?) and meths,
neither of which had any effect at all. Thinking of resorting to a
camouflaging it with a marker pen of vaguely matching colour to the
fabric, as a last ditch attempt.

For some reason, SWMBO hasn't clocked it yet. Have been racking my
brains, but still haven't worked out how I can blame it on the dog yet.

Thanks for all the advice
David