"England" is that part of the island of Britain that is neither Wales nor Scotland.
"Great Britain" was the country's name after the Act of Union of 1707
. In effect, "Great Britain" is England + Wales + Scotland + a few other scattered islands.
"United Kingdom" was the formal name given to the country after the 1801 Act of Union
, which added Ireland to Great Britain. In 1927, after Ireland gained its independence, the UK became "the United Kingdom of Great Britain and Northern Ireland."