I scrolled and didn't see this topic but thought I'd share this savings tid bit.
I was reading a blog about Afternoon tea, and someone commented she used a groupon. I use them all the time here in the States, and looked into Groupon UK. https://www.groupon.co.uk/
I found a great deal for Afternoon Tea at the British Museum, and figured why not save a few pounds while checking out the BM?
So if you're open to trying a new place (and if you're a tourist, everything is new) see if there's a groupon for you to try. They even have deals on tours, including a night time Harry Potter tour, a hop off/ hop on tour, and day trips.