Britannist

The United Kingdom is a Union including Northern Ireland, of course (as has been pointed out). In the event of Scotland unfortunately deciding to leave the UK, then the Union of the UK would not dissolve (as Northumbrian claims in the above quote) - it would simply carry on as a Union of England, Wales and Northern Ireland. But the Act of Union between Great Britain and Ireland (now Northern Ireland) may have to be amended again to take into account the fact that Scotland were no longer part of the Great Britain which had signed The Act of Union with Ireland.

Indeed, the United Kingdom - as a legal entity recognised internationally - could continue even if England were its only member under certain circumstances. And England as the only member of the UK could use the name UK in its membership of international institutions such as the United Nations (UN) where the seating of representatives is decided by alphabetic order. This would enable England's member there to sit next to the person representing that most powerful of nations and our largest single trading partner - the USA.

I would also add that even if the UK did have to formally dissolve due to the departure of Scotland there would be nothing to stop England, Wales and Northern Ireland forming a new United Kingdom and reviving its name. A United Kingdom comprising Wales and England did, of course, exist for centuries before the 1707 Act of Union with Scotland.