What places/cities are you going to visit? Are you interested in museums or other attractions?
The best would be to plan what what to visit and then check the prices online (sometimes it’s good to book the tickets online - you can save money and there are discount codes to use! Especially 241 (two tickets for for one price) for many places in London).
Majority of museums in the UK (including London) is completely free. Some popular places in the other hand are very expensive but then it’s good to check if tourist cards/passes are not a better idea. Examples for London https://www.londonpass.com/london-attractions/
Every big city also offers free walking tours with a guide (with no set price - you tip at the end as much as you want, £5-£10 is absolutely fine), it saves you money and lets explore the place much better! The tours are in English but the tourists always from all over the world, so guides talks clearly and understandable, if you speak any English you should be fine :)
So now it’s your turn to think where are you going to go (in London, without using any discounts, it’s easy to spend over £100 a day just to enter some places if you choose the most pricey ones ;) but choosing mostly free attractions instead will require only £10-£20 a day.. you get the idea :))