In his 2010 autobiography, Keith Richards states that he's still working for Ian Stewart, because to him the Rolling Stones are Stu's band. Here's how it all started, from Keith's perspective:
So, Mick and I had been working with Dick Taylor, backroom stuff, and it's gettin' better. Then we go down to meet Alexis, meet Brian and Stu, and I have the feeling I am grudgingly invited to this rehearsal, for a possible alternative - other band to Alexis and Cyril's setup.
The first rehearsal fot the Stones, or what turned out to be the Stones was at a place called the Bricklayer's Arms, just of Wardour Street in London. It was a pretty exotic area for me at the time. I mean, these chicks walking by in full makep with just a bra on, carryin' a suitcase. It took me a while to figure it out, but they're strippers going from one club to another. They just crisscross, do like half an hour here and another half hour down the street, so they don't bother to dress, just as long as they don't get arrested for indecent exposure, they're just rushing out in their dressing gowns with a suitcase and a wig and the makeup. Maybe it looks great inside of the club but outside not quite so good, these weird masked people coming at you.
I got my guitar in a little plastic case, and I go upstairs and say - some old barmaid was there, typical English platinum blonde with a cigarette, her lipstick smeared - "We're supposed to have a room to rehearse in here". "Upstairs, second floor". I tramp up there and I hear this piano playing, so I follow that. I walk in, and there's Stu sitting there and the piano is against the window and he is playing beautifully as Stu always did when he thought nobody was listening. That's the area where he really breaks out. To hear Stu play under observation is only half of what he is capable of. He was never a showman. It locks him up, to have people watch him, he is his own audience.
Source: Stanley Booth, Keith: Till I Roll Over Dead, Headline Book Publishing, 1994.