Spark plug heat shields ?

[stesrg]

Had a bit of a bad time in removing the Heat shield extensions today had to use force to remove them in fact theirs always one !! I had to destroy it and screw it off ! One out I put a old plug in it got it in the vice and guess what still no joy .
So I guess after a while the clips inside lock onto the plug tips some sort of heating and cooling effect over the years ?

Anyway best I can find is £72.00 a set !! Thought that was a bit steep considering these are made in Germany ?
Anyone got a part number or info where I can get them at a trade price ?
Thank you .
Ste.