Well a big thanks to the various contributors, my bonnet wouldnt open this morning and the tips saved some big bills...here's what i found.
My SIL was a garage mechanic, he suggested almost exactly what bonnetbodger did, get a long screwdriver or implement and first i used the tip to remove the rubber cover that protects the white barrel, it just slides back along the operating 'cable'.
Then use the tip and push quite hard on the white inner at the lock end, operating the key at the same time, you can feel the lock trying to work.
It took many attempts to get the right point, but the bonnet popped up.
Then to get it open properly...same procedure, quite a few attempts to get it right again.
Ideally you want someone with you to lift the bonnet, its hard pressing the screwdriver, turning the key, lifting the bonnet with one pair of hands.
A torch too, so you can see where youre trying to get to.
Once opened, i stripped the lock off, maybe to find i didnt need to. Once stripped, i couldnt get the cable end (white plastic cross) to re-engage. My SIL came round, with everything in place he simply pushed hard with the screwdriver on the same white plastic...and it clicked into place (i'd been trying to do it with my hands)
Thanks all, bonnetdodgers method worked particually well.