Firstly you must buy an Oyster Card (pay as you go) rather than day tickets or travelcard and it will work out cheaper (depending upon the zones you wish to travel) and you can also use them on the tube, buses and water. Secondly, for each trip, before you use the tube, understand (or try) the locations of the tube stations on a map rather than tube map, as some are only a few hundred metres/yards apart and it's quicker to walk. All this will save money as most of central London is all walk able and each trip depends on the zone you are traveling or between. All this means it's hard to estimate but you can also do much planning through the TfL website at www.tfl.gov.uk. Hope this helps, but happy to provide further information - as rough estimate allow £10 a day (to answer your original question) over 8 years ago
Last time I was in London, I bought a daily TravelCard ticket for the Tube (zone 1 + 2 cost GBP 8.40 ) which gave me unlimited access to the tube anytime for all the major sightseeing we wanted to do. It was convenient, but expensive. Sometimes it was clearly better to catch a bus. London's bus system is vastly improved in recent years and we could look out the window (LOL! such tourists!).
I kept thinking that we should have got Oyster cards - then it wouldn't matter what transport we took or whether we used it often enough to get good value.
Here's all the prices for Tube tickets: http://www.tfl.gov.uk/tickets/14416.aspx#
And info about Oyster cards: http://www.tfl.gov.uk/tickets/14825.aspx about 8 years ago
I would also suggest Oyster card.
You will never pay more than £7 a day (during the weekend) when travelling in zone 1 and 2 and £8.40 a day during the week.
Travelcard will cost you £7 / £8.40 whether you use it or not. With Oyster you only pay when you use a bus or tube, hence you can pay less then £7 / £8.40.
Please find more info about London public transport here: http://www.mintytrips.co.uk/getting_around_london_using_public_transport.html
Jacob about 8 years ago