Margate has got the exceptional Ambrette (formerly the Indian Princess); well worth a trip out as the grub is amongst the best posh Indian I have eaten in my life. The service is exceptional and the chef, Dev Biswal, is of Bengali origin and trained in Bombay. His passion for fresh ingredients and inventive flavours will bring him to the Great British Menu one day, mark my words.
Other establishments in Margate are shocking, most notably the Tivoli Tandoori which gave everyone an itchy mouth. Canterbury fares better - the Jalsha and Unique India being passable as far as Keralan food goes.
So returning to the North Indian geographical theme; Benares in Mayfair and Everest in Lewisham. I'd avoid both of these like the plague; Benares is bland and stingily-portioned, Everest is way too spicy for it's own good. My tip for an excellent spicy Thai curry is Thai Square on Putney Bridge. The search for a great curry continues....Venue 5 in Eastcote and Rozana's in Kingston come highly recommended.