I have been to the King Will a few times, once to eat for lunch- I wasn't extremely impressed with the vegan choice, but they were very accommodating. The second time was had drinks to celebrate my engagement- which was lovely and the staff were so wonderful.
Recently I went for a family wedding. My dinner was really lovely and unexpected- I assumed the usual risotto and fruit salad to be served- but they really made an effort to ensure my food was just as exciting as everyone else's. There was so much of it as well that I was actually thankful that they only gave me fruit for dessert! Really something special and they should put the dishes they made me in the main menu as they were lovely.
Cons: not much on standard menu for vegans