Phil,
First of all, to check whether it is the brake plate that is being pinched up, remove the bolt from the rear end of the reaction link and try to rotate the brake backplate. It should turn quite freely - if not, experiment with some paper washers between the top hat bearing and the facing plate. When happy replace the paper with a steel shim of the same thickness. Brake plates seldom are tight, but in the past someone may have skimmed a bit from the top hat in an attempt to rectify rattles from the brakeplate.
Regards,
Eddie.