Hi All. I think Rog nailed it when he says "do you have a way of charging the leisure battery!!!!"
I followed the main hook up to the main junction box and opened it up. Even from my basic knowledge of electrikery I can see there are only two switches in there. I chased the wires, the mains 240 go to the two fitted plugs only. The leisure battery wires lead to the fridge and the auxiliaries ( leds,phone charger and pump). The larger lead goes from the leisure battery to the van battery with a blocking diode fitted to avoid main battery drain. Not a charger in sight!! So, we had been happily running fridge on a full leisure battery for a couple of days and it obviously lost charge. When the van starts up it gets the charge it needs. My basic assumption that there was a charger emphasises the never "assume" anything, it make ass out of u and me.
I did the original suggested check with the AVO meter with a healthy
13v on the leisure battery and of course absolutely no difference when attempting EHU. It has had a good 100 mile return trip recharge so ready for next "short" outing. Thanks for everyone for your advice, I feel suitably embarrassed for ever having asked.cheers!!
Easiest way to deal with the problem of no charger if you want to stay a bit longer would be to get hold of a smart charger, connect it up to your leisure battery and plug it in to one of your mains sockets. I'd recommend the Aldi one if you can get hold of one. Excellent.
You mention an AVO meter. I still have one and use it. It's a model 7 from the 1960s, works perfectly and I use it to check my "cheapo" multimeters I tend to carry around when I'm doing a job.