Thanks for the replys, I already have the calipers, I have fitted the nearside one but the offside one just will not move, neither the union on the actual caliper nor the nut that holds the union onto the metal where it meets the ridgid pipe as I also thought of this like Dojj suggestion.

I have tried a wrench and it just won't move, I even tried a crude method of heating with a gas stove (As I don't have a blow torch) I just don't see what else I can do

I also tried Pauls method of hitting the spanner with a mallet and also tried tightening and loosening, I just don't see what else I can do, as I say I don't want to get to the situation where I round the nuts etc, any more thoughts?

Martin