Chairmen of the Board toured the UK in the Summer of 1971, in October 1972 and again in September/October 1973.
The first tour - the show you probably remember - was criticised in B&S (see attachment from B&S #62). There had been a lengthy article on the group, following their poll win as the "most promising new act", in the previous issue.
I saw them perform at Pickett's Lock, Edmonton on 4 October 1973. Great show, but three very different musical personalities, with Harrison Kennedy being more of a rock than a soul performer. It was good to see General (Norman) Johnson sing live for the first time.
Incidentally, the former member was Eddie Custis.
https://www.thatphillysound.com/copy-of-johnny-caswell
Kesalocasoul's post in Chairman of the Board - Manchester Show was marked as the answer