It's interesting

Is England, Britain, Great Britain and United Kingdom the same thing?

'When people say England, they sometimes mean Great Britain,
sometimes the United Kingdom,
sometimes the British Isles - but never England.'
'How to be an Alien' by George Mikes

"England" is sometimes, wrongly, used in reference to the whole United Kingdom, the entire island of Great Britain (or simply Britain), or indeed the British Isles. This is not only incorrect but can cause offence to people from other parts of the UK.

England	Scotland	Wales	Great Britain

The diverse history of England, Scotland and Wales has led to very different cultural traditions; The Scots and Welsh have right to feel aggrieved whenever the term 'English' is used wrongly, to mean all three.

Countries within a Country

The name United Kingdom refers to the union of what were once four separate countries: England, Scotland, Wales and Ireland (though most of Ireland is now independent).

The United Kingdom

History of the making of the UK

Scotland and England had separate Monarchs until 1603, when Queen Elizabeth I died without any heirs. 

The next in line of succession to the English throne was James VI, King of Scots who became known as James I in England.  James was also King of Ireland and of France at the same time.  He is the King that Guy Fawkes and the other members of the Gunpowder plot tried to kill on November 5th 1605, which is why we remember on Guy Fawkes night.

Scotland and England, together with Wales united by the Act of union passed by the Scottish Parliament and Westminster in 1707 to form the Kingdom of Great Britain. 

The Irish Parliament voted to join the Union in 1801 when the then Kingdom of Great Britain became the United Kingdom of Great Britain and Ireland.  The full name of the UK then changed in 1922 when most of the Southern counties in Ireland choose independence and ultimately became what is now the Republic of Ireland, leaving the UK as the United Kingdom of Great Britain and Northern Ireland.

Source: http://projectbritain.com/britain/britain.htm