Thank all.
I was at Halfords at lunch time , looking for ideas and saw one of those screw type strap wrenches ...
It finally came off just now with what I would consider super excessive force using the spider - the canister now looks like a piece of shrapnel but at least it didnt burst.
I will be checking carefully how much I over turn the new one when fitting. 3/4 a turn after initial contact from memory.
Thanks again
