Well I know you're not supposed to undo and redo locking wheel nuts with an impact wrench, but I did several times and it's always been fine. However, this weekend I went to play with the rear brakes again (I have a sticking brake) and proceeded to remove the wheel nuts with my impact wrench. On one wheel, the nut was looking a bit worse for wear but I tried anyway and the nut just rounded off. On the other wheel, I tried with a torque wrench instead and the lugs in the key snapped off.
So I purchased some Irwin Bolt removers on Amazon Prime: https://www.amazon.co.uk/Irwin-Bolt-Grip-Remover-Expansion/dp/B000QW6K8I/ref=sr_1_1?s=diy&ie=UTF8&qid=1465289282&sr=1-1&keywords=irwin+bolt+grip+nut+remover but they were rubbish. The metal of the nuts is far too soft and they just get chewed up. So now I was left with 2 nuts in a poor state instead of just one. No point buying a replacement key now.
So I took a 19mm hardened steel impact socket and held it in some grips and heated it up until it was very hot. I then placed it over the nut with some pliers and then hit it on with a mallet. I then poured water on it to cool it down and grip the nut as it shrank. I was then able to use the torque wrench and undo the nut easily.
After hammering out the old nut, you can repeat for any other dodgy nuts. It was actually surprisingly easy and as you can see from the picture the metal of the nut is soft enough to allow a heated socket to be hit over it.
The hardest part was hammering out the nut to repeat the procedure on the other wheel!
Anyway, it was always on my "to do" list to remove the locking wheel nuts and replace with standard ones as I've never trusted them and figured one would fail. I just didn't expect to break 2 nuts AND the key in one weekend! I now have 4 standard nuts in their place and will never have issues again
Nick