I went round in circles with the tyre fitters, the dealers and back again - no one could help other than to say they'd have to drill them off!
As a last ditch attempt I googled locking wheel nut removal and came up with a really friendly guy, John, who was based 5 minutes from me in Solihull. He came to my office within 10 minutes and 10 minutes after that, they were off with no damage to the wheel or nut!
I don't know if he's prepared to travel, but his contact details are:
W 0121 733 1965
M 07776 231 952
E info@lockingwheelnut-removal.co.uk
Tell him I sent you his way and good luck!
Si.