Ian Davidson is correct when he says that Trident can't just be moved to an alternative site in England or Wales.

However his suggestion that the fleet could find a new home abroad is misleading ("Nuclear claim over separate Scotland", The Herald, August 30).

The Ministry of Defence might look at some of the last corners of the British empire, such as Diego Garcia. It has its selling points. Adverts showing submariners relaxing on a tropical island could be broadcast to counter the Navy's recruitment problem. But in practice Diego Garcia is a non-starter. The UK effectively sold the island to the US in exchange for Polaris in 1963. The US was then allowed to expand the airfield in the 1980s, in return for supplying the Trident system to Britain.

We could hardly ask for the island back on the grounds that we need it for our nuclear submarines. It is too small to accommodate both a US airbase and a British nuclear depot. In any case, as the 1963 Polaris shortlist shows, remote islands are not suitable locations for a nuclear-armed submarine base.

When the Ministry of Defence decided to buy Trident in 1981 it briefly considered basing the submarines in the US. The option was not pursued for three reasons. First, it would have raised serious questions about the US and UK's compliance with the nuclear Non-Proliferation Treaty. The treaty requires nuclear weapon states to retain control over their weapons at all times. To comply, Britain would have to build duplicate facilities, rather than just using the American ones.

Secondly, concern was that Britain's "independent" nuclear force would be transparently dependent on the US.

Thirdly, the response from Congress would be unpredictable. The special nuclear relationship proceeds under the radar, with very little oversight from senators or representatives. Basing Trident in the US would raise unwelcome local political concerns.

France is even less likely. The Ile Longue base is too small to provide the large safety zones required. Constructing a new British nuclear submarine base in Brittany would be even more difficult than building one in England or Wales.

The more closely you look at the options for Trident, the more you become aware of how the future of the British nuclear weapons programme lies in the hands of the people of Scotland.

John Ainslie,

Co-ordinator,

Scottish Campaign for Nuclear Disarmament,

77 Southpark Avenue, Glasgow.

I note that Ian Davidson MP shares the CND view that closure of Faslane and Coulport would enforce unilateral nuclear disarmament on England too.

The solution is for Scotland to grant England a 49-year lease of Faslane. The Irish Free State gave naval bases to England in 1921. So did Cyprus after independence. Scotland must use Faslane as a key bargaining chip in independence negotiations. A 49-year renewable lease would allow England to remain a nuclear power, thereby retaining her permanent seat on the UN Security Council. This would strengthen our "social union" with England. It would also avoid Scotland clashing with the US, as Washington values the UK vote on the Security Council and the useful political cover of being seen to have allies in foreign policy.

For the SNP, strengthened with a pro-Nato policy, renting Faslane would remove pressure from London and Washington in the run up to the referendum. Those who want an independent Scottish state must remember that all states follow interests, rather than principles.

Councillor Tom Johnston (SNP),

5 Burn View, Cumbernauld.

Dr Willie Wilson correctly quotes the latest issue of Government Expenditure and Revenue in Scotland (GERS), indicating a hypothetical surplus of tax revenue (including North Sea oil) over public expenditure "in and for'' Scotland, and based on a hypothetical UK fiscal balance (Letters, August 27). But he is being a little disingenuous while unwittingly confirming the point that Scotland has subsequently moved into relative fiscal deficit.

The latest GERS figures, as Alex Salmond and John Swinney well know, refer to 2010/2011. The spot price of North Sea oil then was about what it is today ($115 dollars a barrel), but the GERS figures do not take account of the fall in oil output by a whopping 18% in 2011 alone, and it continues to ebb.

Furthermore, in the 2011 Budget, George Osborne increased the rate of supplementary corporation tax on North Sea production from 20% to 32%, hoping to raise an additional £2 billion. Yet despite this hike, the total tax take from North Sea oil (of which only 80% would come to an independent Scotland) fell from £13.4bn to £11.1bn in the year after GERS.

For several earlier years when tax revenue was below public spending in Scotland, the SNP-controlled executive failed to publish GERS. It will be interesting to see what they do when GERS is next due.

There is little prospect of a significant increase in North Sea output because oil price rises will be held in check by falling world economic growth and by the deluge of shale oil and gas production, especially in the US. The UK too has large reserves, especially in England.

To conclude, it would seem that an independence built on the volatile price and output of hydrocarbons would be a pretty dodgy business. And, as Dr Wilson says, it "is right to focus on the economy''. We should also note that other lefty arguments like no Trident and leaving Nato would save nothing but leave Scotland's security free-riding on the UK's goodwill. We should stick with the Union and pay our share.

Richard Mowbray,

14 Ancaster Drive,

Glasgow.