A landing card is an arrival card form that non-EEA citizens are required to complete on entry to the United Kingdom. The traveler must present the completed form at the UK Border Agency immigration desk at the point of entry. The form is usually supplied by the airline, train or ferry company.

In the UK, the landing card system is governed by the Immigration Act 1971, schedule 2 paragraph 5, which states;

“The Secretary of State may by order made by statutory instrument make provision for requiring passengers disembarking or embarking in the United Kingdom, or any class of such passengers, to produce to an immigration officer, if so required, landing or embarkation cards in such form as the Secretary of State may direct, and for requiring the owners or agents of ships and aircraft to supply such cards to those passengers.”

The Secretary of State decides, by issuing a Statutory Instrument, which nationalities must complete a landing card. Currently all EU nationals, and those from Iceland, Norway, Liechtenstein and Switzerland, are exempt. Failure to complete a landing card when this is required is a crime punishable by a fine or six months in prison.

In August 2017, the UK Home Office announced that landing cards will be completely scrapped as part of digital border transformation and modernisation. It is expected this change will come into effect by the autumn.

Information on the card
Typically the information requested on the card includes:

Full name (family name and first name)
Sex
Date and place of birth
Nationality
Occupation
Passport number, place of issuance and expiry date
Flight number or name of aircraft, ship or vehicle
Duration of stay
Port of last departure
Contact address in UK
Travelers are required to sign, and declare the information is true, correct, and complete.

Source from Wikipedia