All I can say is that in the TV programme Gareth Malone was shown with a music sheet headed 'An Old Christmas Card'. My guess is the verse must have been included in the lyrics on the sheet. To me they're very pretty and smooth in keeping with the chorus so maybe Mr Horton wrote them himself but they weren't used subsequently.

I'm going to try and contact Mr Malone and if necessary the BBC. This may take a while, but I'll keep you posted.