Lots of terms for citizens and denizens within the United Kingdom are not interchangeable.

The United Nations and the vast majority of the world define “countries” as sovereign states. England is not a sovereign state like the USA/Russia/China. The United Kingdom is the sovereign state/country, recognised by the UN, that England belongs to. After announcement of the Royal Baby – this interesting news article came on the BBC website:Royal Baby – The American Mistake.I have actually seen websites proclaiming the “future King of England’s” birth – which is particularly funny because there has not been a King of England since the 18th century. The Royal Baby will be the future monarch of the United Kingdom.If anyone has seen the passport of a person from England – you should spot that nowhere on their passport does it say the word England (or Scotland or Wales). The passport clearly states in big gold letters at the top: “The United Kingdom of Great Britain and Northern Ireland” and above that “European Union”.
England was an official country up until the Act of Union 1707 when England merged with Scotland to create “The Kingdom of Great Britain”. Wales had been absorbed in 1535 and was at this time considered part of England. Today, “Great Britain” as a political entity means: England, Scotland and Wales (but not Northern Ireland).
 The history of Ireland is complex and fraught with war (mostly against the invading English).  By the 19th century, Ireland was under British control and in a new Act of Union in 1801 Ireland was joined with Great Britain to form “The United Kingdom of Great Britain and Ireland”. However this new country didn’t last for very long. Understandably the Irish wanted their country back, and they wanted their country be recognized as a real country not a backward province to some imperialist hegemony that thought it should rule the world.
The Irish were successful in gaining independence in 1922. Ireland is now its own country again. It has its own currency (the Irish Euro) and makes its own laws without interference from a higher authority, issues its own passports and belongs to the United Nations in its own right – something that neither England, Scotland or Wales have achieved.  However Northern Ireland remained part of the United Kingdom (and this has lead to decades of violence and conflict).
Thus by 1922 – the country was given its current name: “The United Kingdom of Great Britain and Northern Ireland” or just the UK for short.
So if England (and Scotland, Wales and Northern Ireland) are not official sovereign states – what are they?They can be considered nations and are legally “constitutional countries” but not officialcountries recognised by the international community. These four areas are much more like the US/Australian States or Canadian Provinces than true countries.They have autonomy in certain aspects: e.g. Scotland gets to set its own education system and has its own parliament, can set its own income tax rate. However none of these areas can fully reject the legal authority of the United Kingdom Parliament in London. They are also bound financially to the United Kingdom as they do not get to issue their own currency. Scotland does print its own money but it is still the pound sterling. It is exactly the same currency as that printed by the Bank of England it just has different pictures on the front. You can use Scottish pound anywhere in the UK, though shop keepers down south might give you some weird looks.
 In terms of the military: they have their own regiments but these regiments belong to the UK military. Scotland for example cannot prevent the Scottish regiments from engaging in the Iraq War if they wanted to.
Of course the entire picture is complicated by the fact that Scotland wants complete independence like Ireland and Northern Ireland can’t quite decide. The UK parliament is situated in England, mostly filled with English politicians, and generally makes laws that benefit England. England also has the highest population (by far) out of all four areas, so people can be forgiven for thinking that England is the UK but technically, officially it is not.
However compare this to the state of Texas – it too, is one of the biggest US state, produces a huge amount of the country’s GDP (ranked 2nd after California), has its own government with its own governor who gets to decide everything from education, to state taxes.  The difference is that the government of America is not situated in Austin (or Dallas or Houston), does not comprise mostly of Texans and does not make most of its laws with only Texas in mind or at least one hopes not.
Texas is not the USA anymore than England is the United Kingdom. A person can be both a Texan and an American. I can be both British and English but it’s not the same thing.

The Union Jack
This flag is not the English flag, neither is it the Scottish, Welsh or Northern Irish flag. It is the official flag of the United Kingdom and only the United Kingdom. England, Scotland and Wales have their own national flags (they are technically nations but not countries).  It is called the Union Jack/Union Flag, either name is acceptable. It’s a complete myth that it’s only called the Union Jack if its flying from a ship.
The Union Jack is an amalgamation of St. George’s Cross (England), St Andrew’s Cross (Scotland) and St Patrick’s Cross (Ireland).
Contrary to what you might think at first glance this flag does not have two lines of symmetry. It actually isn’t symmetrical at all – and therefore it can be flown upside down as an insult (though it would only work if the person looking at it had good vision).
 Remember how England is a bit like Texas? The Texans have their own state flag and they are represented on the American flag as one of the 50 stars. It’s pretty much the same with the Union Jack.
On the subject of sporting competitions I will say one thing: having a national football/rugby/whatever team does not make you a country. The World Cup organisers do not have the political clout of the United Nations in recognising countries.
Besides the Olympic committee – deems the UK to be an official country but not any of the individual nations.
As for Andy Murray – the winner at Wimbledon: he is both Scottish and British. He represents Britain when he played at Wimbledon but not England. Many Scottish people have taken offence that recent New York times headline: “After 77 Years Murray and England Rule”.
Other Facts to Bear in Mind

1. Great Britain = England, Scotland and Wales but not Northern Ireland

2. The UK/Britain = England, Scotland, Wales and Northern Ireland

3. The people who live on these islands are British and this is not the same as being English or Scottish or Welsh. Sherlock and John live in England, they also live in the UK. They are officially British, whether or not they think of themselves as English as well is a personal choice.

Ireland is a separate nation, sovereign state, and Scotland is not.