Persons not subject to immigration control divide into two groups.
The first group is those who do not require leave to remain enter or remain in the UK and comprises
(a) British citizens
(b) Commonwealth Citizens with the right of abode
(c) EEA nationals who are exercising Treaty rights
The second group is those who are except from the requirement to have leave to enter or remain in the UK. The groups contains three main classes
(a) diplomats and certain staff of embassies and high commissions and their families who form part of their household.
(b) members of the UK armed forces, members of a commonwealth or similar force undergoing training in the UK at the invitation of the government.
(c) members of the crew of a ship or aircraft, hired or under orders to depart as part of that ship's crew or to depart on the same or another aircraft within seven days of arrival in the UK