Dudley Moore, Peter Cook and Spike Milligan.
I would know more of this. Why is Peter in his jim-jams? Is this a sleep-over panel show? Tell me more!
According to the site this image is taken from, it’s from Not Only… But Also…, but was alas wiped by the BBC:
And, forever turning up like a magnetically erased ghost at the feast of reminiscence, there’s Poets Cornered, the end-of-show I’m Sorry, Whose Clue is it Anyway? progenitor wherein Cook, Moore and guest star try and keep an improvised poem going under pain of being dunked in a pre-Crackerjack tank of gunge. Everyone who recalls this remembers it being screamingly funny, and inevitably not a second of it exists.