Britain's Navy chief on Tuesday warned that an independent Scotland would "damage the very heart" of the service, hitting Scots the most.

Writing in the Daily Telegraph, First Sea Lord Admiral George Zambellas highlighted the pivotal role played by Scotland throughout the history of the Royal Navy, pointing out that almost a third of Admiral Nelson's men at the 1805 Battle of Trafalgar were Scottish.

"I believe that independence would fundamentally change maritime security for all of us in the United Kingdom and damage the very heart of the capabilities," he said.

"While the continuing United Kingdom would eventually adapt and cope, the deeper impact would be felt in Scotland which would no longer have access of right to the security contribution of one of the finest and most efficient navies in the world."

A vote for independence at the September 18 referendum would "greatly weaken the carefully evolved 'whole', as bases, infrastructure, procurement, spares, personnel and training face a carve up," he cautioned.

The comments came hours before Defence Secretary Philip Hammond was due to trumpet the value of a shared defence forces, saying it "provides the security and the peace of mind that underpins almost every single other area of this debate".

Hammond was also to argue that Scottish Nationalist Party (SNP) leader Alex Salmond's vow to expel Britain's nuclear Trident submarines from their base at Faslane would only lead to complex negotiations.

"Alex Salmond knows, as I know, that the future of our naval base at Faslane would be just one of many defence issues that would be the subject of long and protracted negotiations if there were to be a Yes vote," he will say, according to extracts released by his office.

The Royal Navy has 16 ships and submarines and two Royal Marines Commando units based in Scotland.

The three main parties in the British parliament in London -- the ruling Conservatives and Liberal Democrats, and the opposition Labour party -- have shown rare unity in their campaign against independence and for a preservation of the 300-year old link between Scotland and the United Kingdom.

Opinion polls have consistently placed the "no" campaign ahead, but the gap has been closing.