You could try asking website owners if it's okay for you to put a link on your website to theirs. Problem is that here in London there are quite a number of websites just dealing with restaurants and they're in business to make money from customers who book on line etc. So, the way I see it is, if you have a link on your website to one of their restaurant lists, they will only benefit.
http://www.google.com/search?q=london%20restaurants
http://www.first4london.com/directory/Food_and_Drink/Restaurants/Restaurant_Guides/