Just got the car back and they have done an amazing job. Just needs a bit of paint and all sorted. They were extremely careful not to over-spray the underseal, so all is hidden beneath the tailgate.
The workshop manager made a point of coming out to the car with me to show me the repair and also to explain about the struts.
Mine had probably been on the car from new (52 plate), and were sort of working in reverse. By this I mean that they needed assistance to lift the tailgate and, from about halfway would drop with a clunk. The new ones don't - the tailgate rises by itself and needs assistance to shut.
He believes that knackered struts caused my problem.
The new struts are great (and cheap) from flea bay
https://www.ebay.co.uk/itm/2-x-New-R....c100505.m3226
Cheers
Geoff