Tried again today with a longer breaker bar and it's stuck fast. Managed to start rounding the bolt off and destroy two 19" sockets

so I think I'm flogging a dead donkey now!
Will have to take the car to a garage now to see whether they can remove or drill out the bolt and also allow them to fit the struts etc. So frustrating that one nut has stopped me from replacing the strut and will probably cost me +£200 to get sorted...
Thanks everyone for your help.