| Had a few Dave. First attempt is with a torx bit. You'll have to play around with a couple of sizes to get on that's snug, and then tap it in place. Then use an impact driver to try and shock it. Don't just try and turn it. It'll strip out again.
If that fails, drill it. Use a 6mm bit. Just go far enough for the head to come off. Once the head is gone, remove the cylinder and then you'll have some of the bolt to get a hold of. It'll probably come out by hand, but if not get some mole grips on it. | 
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