BB King & Peter Green tapes

[Norton]

Here is a quote from Christopher Hjort's Strange Brew, dated Tuesday 29th April 1969, reputedly made by Doreen Pettifer, secretary of Mayall fan club when B.B. King asked Peter to jam with him on stage at the Free Trade Hall :-
'Come on Peter, show us what you can do,' said B.B.- and Peter did in no uncertain terms! From his guitar came a cascade of notes to shame any guitarist playing blues. It was as if he had been saving his whole life for that moment. Personally I've never heard better from any guitarist. Maybe it all sounded better because it was so unexpected, but my God, Peter should have been proud of himself that night! He has tapes of that jam and we can only hope that one day they find themselves on record.

Have these tapes ever come to light?
Sorry if this has been asked before, but if it has I would love to know the answer and maybe get to hear this.