Might get shot down for this but.......
I used warm water with a TINY dash of fairy liquid. Used a sponge first, then micro fibre cloth. Got lots of grime and dirt off.
Then just warm water with micro fibre, followed by some autoglym leather stuff that was on offer. Came up well, although after nearly 10 months the drivers seat is shiny again rather than the 'matt' look of the rest of the seats.
