Guess I was the lucky one, eh ? The rear undertray came off OK (2 busted replaceable bolts) , easy enough to get to. The straps were then very easy to get to, two straps in a v-shape, same bolt at the front, two separate bolts at the rear. Bolts removed fine, washers behind them a little trickier but as they are only flimsy then a big hammer and a screwdriver told them who was boss. If the new straps don't come with washers then the old ones will reshape easily.
The replacement straps are coming back order, one from a dealer in Warrington and one from Italy as they're not often called for, all in about £20 from Mango's. My local dealer is crap so I called Mango's and he said "Did they try Dealer Search ?" "You what ?" came my reply. This was how they sourced the UK one and discovered no-one else had t'other, hence Italy. Excellent service from them.