FWIW, I did some research on the people claiming copyright breach and there was an e-mail address for "licensing." So I penned a polite letter, explaining the full facts of the situation, and I have just received a positive answer back, which includes an apology.
The reply explained that YouTube do indeed have an automated melody matching system, although how my electronic track even comes close to a proper song, with lyrics and all, beats me...
I also received a notification from YouTube confirming that the copyright claim has been "released."
Thanks for all the helpful messages of help and support above.
cheers
andy