George Osborne has announced a significant expenditure for the upgrade of the Royal Navy submarine base at Faslane. The SNP who oppose the Trident replacement programme have responded with outrage, but their opposition is as usual not clearly defined and is perceived as anti-English in sentiment. There are many good and practical reasons for opposing the Trident programme and the SNP will have the opportunity to make their case in the House of Commons, but they cannot demand a national veto just because the submarines are based on the Clyde in Scotland. The base may be close to heavily populated Glasgow and the potential target for a nuclear intercontinental ballistic missile but moving the base, to say Barrow-in-Furness in Cumbria, would not make them any more safer. Defence is not a devolved issue, it affects everyone in the UK. Even if Scotland did become independent, and based on the Irish example, it is more than likely that Faslane would become a treaty-port. If the SNP wants to gain any traction on this issue they need to be pragmatic and make the argument from an UK perspective.
The main reason why the UK should have the nuclear deterrent is because France has its own independent nuclear deterrent. It is not that France is a threat to the UK, even though the Entente Cordiale does get strained at times, it is about the historical rivalry between the two nations and national pride. The maritime rivalry goes back for hundreds of years and even existed during the Crimean War when the two nations were allies against Russia. Each country still perceived the other as a potential enemy and tried to outdo the other with advances in ship design as they leapfrogged each other in an arms race. The rise of Germany and their naval ambitions was the main catalyst for the Entente Cordiale, with an agreement that France would be the major naval force and power in the Mediterranean Sea while Great Britain would control the North Sea and Atlantic Ocean. This underlying rivalry still persists and to a large extent determines UK defence policy. You may think that this is silly, but it is an important factor in Whitehall especially with regard to foreign policy. The French will only cooperate in joint arms programmes if they can take the lead, otherwise they go their own way with the result that two very similar fighter aircraft (Dassault Rafale and Eurofighter Typhoon) end up being constructed and compete against each other for export orders. The new aircraft-carriers being constructed for the Royal Navy have been designed deliberately to be bigger than France’s carrier. The UK submarines are bigger than their French equivalent. Once you understand this reality it is much easier to fathom what is happening.