I have seen this food festival but only walked past it for a couple of years now and this year we finally went to it. Part of the Tower of London, tickets give you entrance to the Tower too, so essentially a double visit. If you are a Historic Royal Palaces member then of course you can enter for free and don’t need to queue up.
There were bars, street food, food stalls, desserts, a children’s area with good old fashioned fete games, cookery master classes for both adults and children, cookery talks, and live music. The only thing it didn’t have: shade. It was a very sunny day last weekend!
I would say it’s definitely worth a visit if you are a Historic Royal Palaces member, or if you plan to visit the Tower of London on the same day too. I think if you are only planning on going to the food festival then price-wise it may not be worth it, as you have to pay for the food inside too. Saying that, this could be the reason why it wasn’t very crowded, even during peak lunch times.