It is against the law to stay in the UK beyond your time limit, unless:
Otherwise you become an 'overstayer' and you may be prosecuted and sent home ('removed').
The immigration authorities may also deport or remove you for other reasons. They can do this after you have settled here if:
However, you cannot be deported if you become a British citizen (see 'How can I become a British Citizen?').
Also, many Commonwealth citizens living in the UK since before 1973 cannot be deported.