Thanks all. Bit the bullet in the end and got 3 new ones from the batteries mega store near Caen. The old ones were 6/7 year old Elecsols and had been deteriorating for sometime. Decision was made easier when I found I could get 3 deep cycle 120AH ones for 330€.
Don'the know what you did to them Barry but they pretended not to speak a word of English and didn't have time to fit them. Still very happy as I got 30€ discount over on line price for fitting them myself and they came with a 4 yr warranty that I was assured would be honoured by the UK parent company.
Any more details of Battery Superstore at Caen as mine are playing up a bit and heading that way shortly.
After a bit of snow covering solar panel and minus temperatures, mine were down to 12.1v with nothing switched on.
I had both of them tested by Halfords and my local caravan dealer who pronounced them both good but feel they're on their way out.