FTSE 100 or otherwise known as footsie is an index of 100 companies which are listed on London Stock Exchange. In another words these are the companies which are highly capitalised. Their index reflects the well being of the UK economy as the higher the indices are, the better the business prosperity is doing.
Inclusion of a company in FTSE 100 depends on its financial health in terms of market capitalisation for which a threshold of around £1.7 billon is required. There are some other criteria as well which a company has to meet before it can join the group of FTSE 100. The review whether a company should be in FTSE 100 or lower (such as FTSE 250) in regards to inclusion takes place quarterly.
Trading of shares of all companies listed under London Stock Exchange starts at 08.00 and ends at 16.30 GMT.