Thanks for the answers. I did know that Barclay produced paper and now it seems fixer as well. However it never was a paper producer so someone else made its paper and so it seems to be true of its chemicals as well, namely Sangers of Birmingham.

So to those of you with long experience of darkroom work, anyone else used Barclay's fixer( probably U.K. and rest of Europe rather than the U.S.) who can help?

OP, unless the negs are suitable only for the bin I would re-fix as others have advised and there might be no problem with Barclay fixer that a longer fixing wouldn't take care of.

As it is Sangers of Birmingham I think we may need the extensive knowledge of a West Midlander called Ian Grant to get to answers as to its origins etc a

OP, the itching might be peculiar to this make of fixer, in which case not a large problem or it might be that you are allergic to the chemicals in fixers in general in which case a much bigger problem. However
if you avoid its contact with your skin which is do-able then you should be OK