I sent my entry to Crufts (myself and OH as owners), and also ordered an additional pass at the same time.   When my tickets came I was really surprised to get a helpers ticket which I had not asked for.    Would this be because we are down as joint owners?  Only now it seems I have a spare ticket.

Yes :) all joint ownerships will get a "helpers pass"!

I did exactly the same the first year I ended up with 7 tickets for 5 of us :)