Mick didn't get to choose the Auden quote. He was simply asked to read it.

So he played the naughty schoolboy and used a silly accent to gently
send-up the pretentiousness of how they're handling this anniversary

If you were still in grade school, you would have gotten the joke immediately

Marianne Faithful:

I remember going to a dinner with Wystan H. Auden.
In the middle of the evening Auden turned to me and, in a gesture
I assume was intended to shock me, said, "Tell me, when you travel
with drugs, Marianne, do you pack them up your arse?" "Oh, no,
Wystan," I said. "I stash them in my pussy."

This was the same dinner where the politician Tom Driberg tried to
convince Jagger to stand as a Labour candidate, punctuating his
offer by fondling Mick under the table.

Quite a few sources say that Bob Dylan ripped off Auden's poetry
repeatedly, including rhythms and verse structure...

And more than one source claims that Paint It Black was inspired by
Auden's Funeral Blues, especially the last verse...