While The Tamarind is a fine Indian restaurant indeed, I would recommend the following as excellent alternatives:
1. Zaika in Kensington (www.zaika-restaurant.co.uk), which is the other Indian restaurant (along with The Tamarind) with a Michelin Star;
2. Benares in Mayfair (www.benaresrestaurant.com), the owner and head chef of which was the one who years ago helped The Tamarind get its Star; and
3. The Cinnamon Club in Westminster (www.cinnamonclub.com).
Chutney Mary's is also supposed to be good, though unlike the other three, I have not dined there, so I cannot say for sure if it is good (though there's no reason for me to think otherwise).
Whichever one you choose, I hope it doesn't make a liar of me!