Answer:
1: Some time around 1948 and 1970
2: If you arrived in the UK from a Commonwealth country before 1973 you had the right to stay in the UK.
3 : On the 22 of June 1948, a ship called the MV Empire Windrush arrived at Tilbury Docks, Essex bringing workers from Jamaica, Trinidad, and Tobago.
3 a: hostile environment policy is a set of administrative and legislative measures designed to make staying in the United Kingdom as difficult as possible for people without leave to remain, in the hope that they may voluntarily leave.
3 b: ?
4: Those with no proof of documentation where sent out of the country.
5: ?