What will be the fate of "Britain's" nuclear deterrent if Scotland becomes independent? If the result of the Glenrothes byelection on November 6 mirrors that of Glasgow East, an answer may soon be needed. This is the biggest conundrum among a series of challenges concerning Scotland's stance on defence if the country were to become an independent state - leaving England, Wales and Northern Ireland (EWNI) as a separate independent state.
Defence is a fundamental attribute of statehood. Yet "Britain's" nuclear forces, which are supported by MPs and the general population in EWNI, are situated in Scotland. They are not supported by either the Scottish people or the Scottish parliament. Nor did the Scots support Britain's invasion of Iraq. The SNP's defence stance reflects both concerns.
The submarines housing the Trident missiles are based at Faslane, near Glasgow. The nuclear warheads are stored at Coulport. The manifesto of the Scottish National party in the 2005 Westminster elections states that an SNP government of an independent Scotland will wish to move the Trident fleet and the nuclear warheads from Scotland. They would need to be relocated, probably Devonport in England. Whether the Trident force will be worth the extra expenditure required to set up new facilities will be a difficult problem for an EWNI defence budget under strain, although it would no doubt insist on Scotland sharing the cost of rehousing the base in any eventual agreement between the countries.
As for conventional forces, the SNP wishes Scotland to continue to be a member of the European Union but not Nato - that is, it would follow the Irish example rather than the Danish. If Scotland withdraws from Nato it would become the first state to leave the alliance since it was formed 60 years ago.
Scotland would have to decide whether to keep Scottish battalions and marines in Afghanistan. The International Security Assistance Force (ISAF), the Nato-commanded military force, is authorised to deploy in Afghanistan under UN security council resolution 1776; it includes troops from 40 countries, many of which are not Nato members. The 2005 manifesto says that Scotland can participate in UN-authorised peacekeeping. So presumably Scottish forces can stay in Afghanistan.
Both Scotland and EWNI will be the successor states to the UK under international law and both will be entitled to be members of the UN. EWNI will presumably claim the permanent seat at the UN security council. As for the UK's status as a nuclear weapon state under the nuclear non-proliferation treaty (NPT), there is a precedent: on the dissolution of the Soviet Union, Russia became the successor nuclear weapon state while Ukraine and the other former Soviet republics became non-weapon states. Thus Scotland would follow Ukraine's example and apply to the International Atomic Energy Agency for a safeguards agreement as a non-weapon state under the NPT.
There is unlikely to be any opposition to this provided that Scotland and EWNI agree the transitional arrangements needed to transfer the Trident base and warheads from Scotland to their new location. During the transition period the base and weapons can remain in Scotland without affecting its status as a non-weapon-state under the NPT provided there is no transfer of ownership and control of those weapons to Scotland.
The SNP Conference in Perth this week will have plenty to discuss. Their decisions could reshape the strategic map of Europe.
Norman Dombey, professor emeritus of theoretical physics at Sussex University.