I'm an Englishman from the Midlands with some Scottish heritage who is currently on holiday in Scotland - somewhere my family frequents. As an Englishman and UK citizen it has been very alarming to see how the issue of Scottish independence has been discussed and debated in Scotland. The most important issue has not been raised in the debates or by the talking heads on TV. How the UK government will negotiate in the case of Scottish independence.
(1) Capital Flight
If the Scots do decide to go independent they will firstly be in a very weak negotiating position. The Scots will have to negotiate to get the pound. During the negotiations there will be massive uncertainty and there will be significant capital flight from Scotland to Britain (as Britain will be seen as a safe bet). This will obviously be to the benefit of the British, so during negotiations the British will deliberately drag them out and induce uncertainty so that wealthy Scots in Edinburgh and Aberdeen move the money at least down to Leeds and probably into London.
(2) The British will negotiate very tough terms
If the Scots insist on keeping the pound there will be massive costs to pay for that. Obviously the shipbuilding, submarine building, UK tax collection work and various UK government operations will be moved South as soon as possible. The UK may insist on receiving some of the tax revenue from North sea oil. They may also insist on the Scots bearing significant debts of the UK government (the UK will definitely play the card that it was the Scottish banks - RBS and HBSO - that got us into recession). The UK will also block the Scots entry to the EU until they get what they want.
A Scot reading this might think this is all hokum and the UK gov wouldn't do this. The problem is that in England there is strong feeling that foreigners (the EU) are screwing the UK over - vis a vis UKIP. An incumbent UK government would play hard ball with the Scots (a now foreign nation) to show their strength in negotiating terms for the UK .
(a) if David Cameroon is in power he will screw the Scots over partly because the Tory party won't care about the Scots once they leave the union and because Cameroon needs to appear strong in foreign negotiations to undermine UKIP
(b) Ed Milliband will face similar pressure to appear strong in negotiations with foreign countries - and let's remember that Ed Milliband is willing to really screw people over, remember his brother...
(3) Remember what forced you into the union
The reason why Scotland and the UK came together was because the Scottish tried to build a strong nation to compete with the English. The Scots made risky investments into South America - the Darien scheme - to do this. This risky speculative endevour went terribly wrong, the Scots were completely broke and were forced to accept unification with the UK in exchange for reinstating the wealth of Scotland (at the expense of the English it is worth noting).
There are parallels between the Darien scheme and Scottish independence. Both of these were and are, respectively, stepping into the unknown, taking a big gamble on an otherwise decent situation - and ultimately, both end up with the English getting what they want.
If you are Scottish and thinking of voting yes - and you think England has been screwing the Scots over since the union - how'd you think the English will treat you if you betray them?