"8A Persons ceasing to be exempt (1) A person is exempt for the purposes of this section if he is exempt from provisions of this Act as a result of section 8(2) or (3) (2) If a person who is exempt- (a) ceases to be exempt, and (b) requires leave to enter or remain in the United Kingdom as a result, he is to be treated as if he had been given leave to remain in the United Kingdom for a period of 90 days beginning on the day on which he ceased to be exempt."
"Where a person having limited leave to enter or remain in the United Kingdom becomes entitled to an exemption under this section, that leave shall continue to apply after he ceases to be entitled to the exemption, unless it has by then expired..."
"In the case of [any form of entry clearance to which this paragraph applies], it shall have effect as leave to enter the United Kingdom on one occasion during its period of validity; and, on arrival in the United Kingdom, the holder should be treated for the purposes of the Immigration Acts as having been granted, before arrival, leave to enter the United Kingdom: (a) in the case of an entry clearance which is endorsed with a statement that it has to have effect as indefinite leave to enter the United Kingdom, for an indefinite period; or (b) in the case of entry clearance which is endorsed with conditions, for a limited period, being the period beginning on the date on which the holder arrives in the United Kingdom and ending on the date of expiry of the entry clearance."
"(1) Subject to paragraph (4), an entry clearance shall only have effect as leave to enter if it complies with the requirements of this article... (2) The entry clearance must specify the purpose for which the holder wishes to enter the United Kingdom. (3) The entry clearance must be endorsed with (a) the conditions to which it is subject; or (b) a statement that it is to have effect as indefinite leave to enter the United Kingdom."