Holding the United Kingdom together will be an "enormous challenge", Britain's most senior civil servant has warned.
Cabinet Secretary Sir Gus O'Donnell said the question of whether the UK stayed together would be a major issue in the coming years.
His warning, on the eve of his retirement at the end of the year, comes as the SNP administration in Scotland is committed to holding a referendum on independence before 2016.
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."
Sir Gus said 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.
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."