As a location, the UK is horribly overpriced and London is the worse. On the other hand, the UK has some of the most spectacular sights in the world and is well worth the cost.
Having said that, there is quite a bit that you can do to bring the cost down.

I hope you find these tips handy

Travel Insurance: Everybody needs some travel insurance, if you lose your baggage or get hurt the bills can pile up quickly. I suggest you get some basic cover and buy that cover online. Do not buy from a travel agent, they will overcharge you.

Cheap Food: If you have a kitchen cooking your own food is best. Go to Tesco and buy some Tesco brand food. The store brand food in the UK is the cheapest and of high quality. If you can’t cook try a pub lunch, just stay away from restaurants.

Getting Around: The cheapest way to travel is the public transport system. If you are staying for a short time, that means buying a day/week travel card. The card will be for the zones, in which you are traveling(London has six zones, zone one is on the inside, zone six is on the outside).If you are staying longer the cheapest thing to do is to buy an oyster card. Both can be bought at the tube station and allows you to ride the tube and buses.

Information: Once you get to London, go to a shop and buy a “Timeout” and a “London A-Z”. You should be able to buy them at any shop in London. The “London A-Z” is a map paperback of London, it has a tube map in there. The Timeout is a magazine and you will find all upcoming events in there.
Both are critical to enjoying your stay in London.

Accommodation: If you are staying for a short time, the cheapest thing to do is to go to a backpackers hostel (I suggest the Earls Court area, it’s on your tube map). If you are staying for longer, look for a house share, with people of your own nationality. You will need to shop around online for good bargains, in both cases.

Traveling outside London: The cheapest way to travel outside London is by train. The key, in this case, is to buy the ticket wayyyy before you travel. This will bring the price down with up to 75%. You can purchase tickets online, by phone, or at any rail station in the United Kingdom.

Go in winter, spring or fall: Though most things are cheaper in the off season, you will save the most on your plane ticket.

What To Do: What can you do entertainment wise, on the cheap? Read 10 things to do in London on a budget to answer that question. The biggest tip is the free museums.