- Sir Gus O'Donnell said Westminster will face 'enormous challenges' holding the union together
- SNP has promised to hold a referendum on Scottish independence by 2016
- Alex Salmond says Sir Gus is 'right to raise the constitutional issue'
- Sir Gus lists keeping Britain out of the Euro against Tony Blair's wishes as one of his proudest achievements in wide-ranging interview
By Rob Cooper

Britain could break up within years and Scotland could become an independent nation again, the country's most senior civil servant today acknowledged for the first time.
Cabinet Secretary Sir Gus O'Donnell said that whether the union could be maintained would be a major political issue in the years to come.
Alex Salmond, the Scottish First Minister, has vowed to hold a referendum on independence before 2016.
The SNP won a majority at Holyrood for the first time raising the spectre of the break-up of Britain.
Although David Cameron has pledged to keep the union together, Sir Gus wrote in a wide-ranging newspaper article today that it will be a big political issue in the years to come.
Critics think it is is unlikely a majority of Scots would vote for independence. However, the devolved Scottish government could be given additional law-making powers.
Sir Gus's remarks come before he retires at the end of the year.
Writing in the Daily Telegraph, Sir Gus said: 'Over the next few years, there will be enormous challenges, such as whether to keep our kingdom united.'
This morning Alex Salmond said that the civil servant was right to raise the constitutional issue and said he wanted to 'win the fight' for independence.
He said: 'I have always regarded Sir Gus O'Donnell as a model civil servant, who has been extremely fair in recognising and respecting the democratic mandate of the Scottish Government.
'Sir Gus is right to recognise the importance of the constitutional issue, and the SNP Government are up for the challenge of building and winning the case for Scottish independence - unlike the Westminster parties, who seem to have their heads buried in the sand.'
Scotland has been united with England since the Act of Union in 1707.
However, after Tony Blair devolved law-making powers to Scotland following a referendum, calls for independence have grown.



Critics warned at the time that once the Scots had their own parliament it would put Britain on a slippery slope towards break-up.
In the years ahead, MPs at Westminster must also tackle the West Lothian Question.
Scottish MPs can vote on education and health laws at Westminster but English MPs do not have the same powers over Scotland.
A commission has been set up to find a solution to the constitutional anomaly.
As well as tackling the issue of whether the UK will break up, Sir Gus wrote in his piece today that the Civil Service needed to overcome its 'cultural inertia' and take a leading role in driving economic recovery.
'It is not enough now for the Civil Service simply to respond to a dampened economic climate: it needs to become a central part of its recovery and growth,' he wrote.
Sir Gus also said he believed successive governments had been too quick to address problems with regulation and legislation.



He encouraged ministers and civil servants to be more creative in solving problems, urging them to take more risks and have a 'grown-up approach to failure'.
He said civil servants had risen to a challenge set out by the Prime Minister to do away with unnecessary regulations, having recommended scrapping more than half of the 1,200 rules they had looked at so far.
Sir Gus also wrote of his pride over the 'thorough, evidence-based analysis' carried out under the last government, which resulted in Britain staying out of the euro.
'Without that, the challenge would be substantially greater,' he added.
He listed keeping Britain out of the euro against the wishes of Tony Blair as one of his proudest achievements.
Earlier, in an interview for Channel 4 News, Sir Gus disclosed that Whitehall had carried out contingency planning in case the coalition breaks up - although he said he believed it would run its full course to 2015.
'My reading of the coalition, the relationship between the Prime Minister and the Deputy Prime Minister, is that is probably when the next election will be,' he said.
'You have to do contingency planning, but I think our main scenario is that we go through to 2015.'