Plenty of historic sights in London but London is a dirty, expensive and violent city (many more murders than New York) so be careful and do not stray off the tourist areas. Street crime with knives is very common, do not resist just hand over your money.
Really be careful and you will enjoy a day or two in the "tourist" capital then get out and see some of the safer places such as Bath (110 miles away), Oxford (50miles) and maybe even Cardiff the Welsh capital - a compact clean city much friendlier and cheaper than London.
Rail transport is quite expensive unless you can book ahead so consider coach transport - National Express is the main one and you will see more of the country.
Source(s):
lived here for many years and seen this country go downhill