The London School of Economics (LSE) offers bachelor's degree in law, management, economics, other social sciences (sociology, social anthropology, political science) , international relations, and some humanities subjects (e.g. history and human geography). A complete list of majors may be found here
. Imperial College London
on the other hand specializes in engineering (all fields), physics, chemistry, biological sciences, mathematics and statistics, computer science, and medicine.
Finally, University College London (UCL) is a general university
, offering pretty much any subject you can think of.
LSE and Imperial are very selective, especially for some particular majors, and your chances of admission are slim. I don't know about UCL though.
There are also several other less prestigious colleges in London that you might look at besides the ones I mentioned above. Please check "London Colleges" in the UK site "The Student Room".