I’ve been to London only once back in 2017, but I did have meals at several South Asian restaurants and enjoyed them all.
Dishoom, which I believe is inspired by Mumbai Parsi cafes [London] Dishoom
Lahore Kebab House [London] Lahore Kebab House
Tayyabs [London] Tayyabs
Hoppers (Sri Lankan hoppers) Hoppers [London] - #6 by Mr_Happy
More upscale - Gymkhana [London] Gymkhana