Stamper,
Imagine this. Scotland votes yes. Milliband then declares no currency union as a manifesto promise which will leave both the labour voters in England & Scotland worse off. What a slap in the face to loyal Scottish voters.
The situation would be worse than you describe. If Scotland votes Yes then it will remain a part of the UK until nominally 2016. In other words, Scotland would be a part of the UK at the next General Election in 2015, yet all three unionist parties would have as part of their manifesto a pledge that purportedly would be in the best interest of the rUK rather than the UK. It would be wilful neglect of a part of the UK they were elected to represent.
I suspect there is a large oilfield that has been discovered that they aren't telling us about.
Just the one?

There are reputed to be vast oil and gas fields in the North Atlantic Margin that have yet to be tapped. Apparently the largest field in the world lies a short distance off the coast of Lewis. In addition, the MoD is known to have blocked exploration of oil in the Firth of Clyde waters.
Presumably you are aware of the McCrone Report?
Voting trends differ with every election. Ukip is on the rise and will take a large share of the vote and we are into a particular time period where hung Parliaments could be the norm. So 29 seats will be crucial to Labour. Image an England free from Scotland and there is an election that the Tories win by a dozen seats.
Yes, it is certainly the case that when the result is close, Scottish votes can influence the result.
John,
Gibraltar isn't actually a country, nor are the Isle of Man or the Channel Islands
Nor is Wales, which is a Principality.