In the civil jurisdiction, you have to go quite a long way to be in contempt. IF the claimant was legally represented, he should not have made such allegations without sound evidence to back it up - that can be dealt with by way of adverse costs and a professional complaint.
What exactly did C say?
Did he say "that is not my signature" ergo leading to the inescapable conclusion that it was a forgery
or did he say "D forged my signature on x date at y place"?
Either way, the finding of the land tribunal will be paramount. IF the land tribunal finds for him, you are never going to get home on contempt. IF the land tribunal finds for you, their findings will be important. There is a world of difference between "I do not accept the evidence of C" and "C has fraudulently produced evidence as to blah blah". I would guess the more likely finding to be "I do not accept the evidence of C".
Personally though, I wouldn't bother. In the civil courts, contempt is dealt with by way of a High Court action. Its going to cost you a shed load of money for little outcome.