The difference between the UK, Great Britain and England is that England is one of the countries which makes up the British Isles.
And the United Kingdom is the political unit that consists of England, Scotland, Wales and Northern Ireland.
Great Britain is the geographical term that refers to the island that is known simply as Britain.
England also ceased to exist as a separate sovereign entity and became part of the Kingdom of Great Britain, along with Scotland, on May 1st 1707, following the Acts of Union.
The Acts of Union merged the Kingdoms of England and Scotland into a single entity and formed the Kingdom of Great Britain.
As a result, England no longer functioned as a separate political entity with it's own parliament, which instead became merged into the Parliament of Great Britain that is located in Westminster, London.
And the Treaty of Union, agreed upon in 1706, laid the groundwork for the Acts of Union, which were then passed by the English and Scottish Parliaments.
Then the newly formed Kingdom was later expanded to include Ireland as the United Kingdom of Great Britain and Ireland in 1801.
And following the Irish independence in the early 20th century, the name was then changed to United Kingdom of Great Britain and Northern Ireland, which is still the official name.