This second selection from the Secret Policeman’s Ball is my actual favourite, and is probably more widely known than the Peter Cook sketch I posted earlier.
It features a young Rowan Atkinson portraying a somewhat ‘disaffected’ English teacher in a British public school (which actually means ‘a privately-owned school which you have to pay for, but which doesn’t place restrictions on who can attend beyond that’). This is quite possibly my favourite comedy sketch ever.
In the deadpan delivery and the acidic tone of the character, you can see the genus of Atkinson’s famous work in the sole use of mannerism and atmosphere to create marvellous comedy. He recorded a lecture (much of it in the form of a demonstration) on the subject which is absolutely astounding to watch, if you can find a copy anywhere (my brief search located only the above link, sadly).
