I started to fit a set of roof rails to my Freelander 2 today and got the front bits drilled and the new bolt system in place to make the front bracket but had a little trouble with the back.

At the back as you know there are 4 nuts protected by Fir Tree Plugs and they just won't come out. I've managed to snap the top off 2 of them already and I'm pretty sure the other 2 will do the same.

Getting the plastic out and the threads functional is of course my next task and I have slowly drilled out as much plastic as possible and will get hold of a tap to clear the threads up but does anybody else have any other suggestions and possible options that may help me get the other 2 out without them breaking?

Hacksaw cut a groove in them, and unscrew with a flat screwdriver

Cheers mate, it's a good tip but these are in solid and because they are plastic they just sheer off.

Being recessed means you can't actually get at them very easily but on the broken off ones I tried tapping the tip of a screwdriver into the plastic and twisting it and that just made more plastic crumbs.

Borrowed a mate's tap and die set today and it was a doddle to clear the threads. Simply drilled down with a 1mm bit a few times to loosen the plastic and then re-tapped with an M6 to clean up the threads.

Getting that crossbar on is a fiddly job though - given up for tonight.