Thankyou SWBKCB. Wikipedia has the picture of PROC, just as I remember her. This site also states that leasing out one of its aircraft led to its downfall. I wonder if there were additional factors?
I'm sure I read somewhere that the ex-Britannia 737, G-BAZI, was infamous on account of reliability issues with her former owner. Perhaps this, plus the growing 767 fleet, made BAZI an obvious target for disposal. I don't know how well she behaved with Airways Cymru and any subsequent owners.