IN the event of a nuclear war between the Soviet Union and the west, key members of the British Government would have survived on ships specially built by Caledonian MacBrayne as 'floating nuclear bunkers', and hidden along the Scottish coast and in lochs.

There is also speculation that the Royal Family would have been evacuated to one of these CalMac survival ships to last out the war.

The revelations about Scotland's role after an atomic war appear in top secret documents which have just been declassified following Freedom on Information requests from Cold War researcher Mike Kenner.

The papers detail the “Python” programme designed to keep the government running and the head of state alive in order for the British state to continue operating despite a nuclear exchange, mass deaths and radioactive fallout.

Kenner said: "According to a 2009 Cabinet Office statement, 'The Python plans that were valid from 1968 bear similarities to plans that are still current.' This explains why it has taken almost 50 years for the Cabinet Office to release any substantive information concerning the Python concept."

Britain’s early Cold War planning was shaped by the experience of the Second World War. Evacuation still played a part as did tin hats and ladders, with the Women's Royal Voluntary Service ready to dish out soup and blankets, but gradually planners had to accept that the advent of the hydrogen bomb had made such measures redundant. The 1955 Strath Report, which considered the potential effect of the new bombs on Britain, warned of 12 million deaths and war “beyond the imagination.”

Thinking began to change. The Civil Defence Corps was disbanded in 1968 and plans to evacuate the cities were shelved. Glasgow had previously had a detailed evacuation scheme which involved gathering its “priority classes” – children and pregnant women – at local assembly points such as Ibrox Stadium and the Kelvin Hall before loading them onto trains.But these schemes were abandoned in favour of a “stay put” policy.

But staying put was not for the politicians, or the Royals. From local councillors to the Prime Minister and the Queen, those in power were still able to flee the cities or retreat to a bunker.

Central Government had a huge bunker in Corsham, Wiltshire. Formerly a stone quarry, later used as a huge underground aircraft factory in the Second World War. The site, codenamed Burlington, was a vast labyrinth capable of accommodating 4000 people, complete with roads, street signs, a medical wing, BBC studio and coffee bar.

But the Cuban Missile Crisis of 1962 prompted Whitehall to question its suitability. If nuclear war seemed imminent and Burlington went operational only for the crisis to defuse, its location and purpose would have been revealed. There were also suspicions that the Soviets already knew about it – suspicions seemed to be confirmed when it was later revealed a Soviet satellite flew over the site daily.

So a radical new plan, Python, was formed which took the opposite approach to Burlington. Rather than gather the Government in one location, they would be dispersed around the country in organised autonomous groups where they would sit out the nuclear war in “protected accommodation” in the hope that some of them would survive and could link up afterwards, allowing the British state to continue to function.

The Python plan began operation on May 1 1968 and was classified Top Secret. A Memorandum of the same year noted “the details of these dispersal plans [Python] are among the most vital of Britain’s state secrets.”

Python was so sensitive that many in Whitehall who worked in Cold War planning did not know about it. They believed Burlington, by now given the new code-name Chanticleer, was still the nuclear escape plan and the Government fostered this belief by keeping Chanticleer operational, allowing it to act as a decoy. Its equipment was maintained and its ration stocks topped up but the only role this massive bunker would now play in a nuclear attack was to offer the surviving Python groups a potential meeting point after the war.

The secret Python dispersal locations were: Culdrose in Cornwall; HMS Osprey in Portland; University of Aberystwyth; Taymouth Castle in Perthshire, and either the Royal Yacht Britannia or HMS Engadine who’d embark her Python group at Loch Torridon or Oban.

Alongside these Python teams were 'Support groups' - designed to help keep civilian survivors alive - and once again these proved Scotland’s essential role. There were six in total, either working for the United Kingdom Supply Agency (UKSA) or the National Air Transport Agency (NATA) and half of these groups would have taken refuge in Scotland, initially at the Bridge of Don Barracks, Aberdeen; Fort George Barracks, Inverness and with another at sea on a specially-built ship run by Caledonian MacBrayne.

In 1964, the Secretary of State for Scotland had ordered three of these nuclear ships to be built. These were the Columba, Hebrides and Clansman. They were chartered to Macbrayne Ltd where they operated as ordinary car ferries but they had extraordinary features making it possible for them to act as floating nuclear bunkers.

Each ship had massive guillotine-style doors which could seal the car deck. The external doors and vents were air-tight. There were decontamination rooms with showers. The air pressure could be altered to repel external contamination and the exterior of the ship had sprinklers so that fall-out could be washed away.

In the event of a nuclear war one of these ships would have hosted a UKSA group whose duty was to obtain and distribute supplies to a devastated Britain. They would have surveyed the country’s food stocks and surviving agriculture, assessed the food requirements of the regions given that the country’s population would have been in flux, with previously empty regions now likely to be filled with refugees from urban areas, and they would have arranged the procurement of supplies from overseas.

The importance of the UKSA groups, such as 'Whiskey' Section destined for the CalMac ship, cannot be overestimated and a Whitehall memorandum noted that without a surviving UKSA group Britain “would cease to exist as a country”. So the relative space and emptiness of Scotland was essential to the British government. Half of their dispersed groups would have escaped here.

The Calmac ship wouldn’t have sheltered politicians. It would have held experts in shipping, communications and oil distribution, plus trade advisers in areas such as meat, milk and cereals. The Ministry of Agriculture, Fisheries and Food quietly surveyed people from these fields, drawing up biographies of likely candidates and assessing their education, their CVs, and also their character. There were notes such as “he would thrive on adversity” and a remark that another was keen on rugby and had been capped for Scotland. Lord Sainsbury was suggested as a suitable candidate to be in charge of meats but was deemed “too old and gentle”.

Whilst these UKSA advisers would have been discreetly told of their nomination for war service, the civil servants in the Python groups would not have been informed until the last minute when they would be handed a letter saying they were to participate in “special duties outside London” and should immediately go home to pack a bag. They would then gather at a designated assembly point and be taken to their secret Python location after being warned to travel in “as inconspicuous a manner as possible.”

The Whiskey Section destined for the CalMac ship would have journeyed from central London to RAF Benson, Oxfordshire, from where they’d have flown to RAF Dalcross (now Inverness Airport) before travelling by rail to either Oban or Mallaig. There, one of the Calmac nuclear ships would take them to an unspecified sea loch where they’d remain throughout the nuclear war. Once it was deemed safe to move they’d link up with any surviving groups at Chanticleer, the old bunker in Wiltshire – or at another location if Chanticleer had been destroyed.

Not only would the CalMac ship have been loaded with radiation equipment, rations and approximately 130 people but it might also have been packed with money. A memo from the Treasury in 1968 noted that “money, in the form of both notes and gold, might be needed to be held in Python groups and National Agencies Sections for central government purposes”.

And after the war, if the ship, its passengers and its gold had survived, the staff would begin trying to supply Britain with food and oil.

Mercifully, these plans were never needed and the three nuclear ships avoided being called to their wartime role. They carried on taking passengers and cars to the Scottish islands until CalMac sold them in the 1980s. Clansman went to Malta and then into service on the Red Sea. She was last seen abandoned off the coast of Sudan and her ghostly hulk can be spotted on Google Earth.

The Hebrides was sold for demolition and went to Turkey. Only the Columba remains in Scottish waters, sailing as The Hebridean Princess, having been sold in 1988 to Hebridean Island Cruises.

The chairman of the company confirmed to the Sunday Herald that she no longer has the ability to act as a nuclear bunker and that all her nuclear features were removed prior to sale.

The three Calmac nuclear ships have gone their separate ways but speculation remains as to why three were built. It’s clear now that one was for use in the Python concept, but what of the other two?

It had long been rumoured that the Queen would be evacuated on Britannia, but as this would have been required by the Government it’s a reasonable assumption that she would have been given use of one of the Calmac ships.

Indeed, the Queen is familiar with them, having holidayed on The Hebridean Princess and its current owners display the Royal Warrant.