i know it is possible to break it off with a chisel and hammer, or some tools like that lol. obviously quite a drastic thing though. i think cockney_si's idea of going to a garage would be good!
my local garage took 8 hours to remove a locking nut on a fiat once, i would expect u to ask them before they have a look in case they charge u to take it off
you should be able to knock an old socket or one you dont mind damaging onto it, it has to be quite a tight fit, and then undo it with your socket wrench.
This is assuming you are prepared to replace the locknuts afterwards.