The United Kingdom is the nation state, Great Britain is the combined land mass of Britain and the island of Ireland, England is one of the 4 home nations.
Great Britain does not include Northern Ireland. This raises the question, "what is the difference between Great Britain and Britain?"
The distinction, when it is made, is that Great Britain is the entity encompassing the three nations on the island of Britain. Sometimes the distinction is not made, and in that case Great Britain is used for both.
The United Kingdom is the nation state, Great Britain is the combined land mass of Britain and the island of Ireland, England is one of the 4 home nations.
Great Britain does not include Northern Ireland. This raises the question, "what is the difference between Great Britain and Britain?"
The distinction, when it is made, is that Great Britain is the entity encompassing the three nations on the island of Britain. Sometimes the distinction is not made, and in that case Great Britain is used for both.