Taste London

It is more worth it for those that live in London than those who are visiting.  It gives you great discounts off many restaurants in London but the initial cost is about £70 so you need to use it a few times to be worth it, click here for more details .

have fun

The card is expensive.  Try the Indian restaurants and seafood places.  Ask a Londoner for their recommendations.  DON'T forget the pub food.  It can be really, really good.  My husband and I like to shop at the Food Courts at Herrods, Sainsbury and others, and take it to the park or back to our rooms.  The food is spectacular, and you can watch your budget.  It is not particularly cheap, but you can buy small portions.

Tastelondon is a very good card but you do need to use it a few times to get the value. You can however get it at a discounted price of £49.99 here  https://www.tasteuk.co.uk/ssl/purchase_join.php?al=visitlondon and enter the promo code visitlondon.