And some leading UK public sector figures are planning jobs cuts of 15% or more, it was claimed.

Consultants PriceWaterhouseCoopers (PWC) warned urgent reforms in working and delivering services were needed to avoid more “draconian” cuts in future.

The warning came in an updated report on the scale of the public debt problem facing Britain as a whole.

The report sets out a range of tax and spending options - keeping current spending plans but raising taxes up to a level of around £26 billion a year, avoiding tax rises but cutting spending by as much as 23% if health spending is to be shielded, or spreading the fiscal burden evenly between tax rises and spending cuts.

The experts said Scotland would be particularly hard hit by a public sector recession as the public sector in Scotland already accounted for 50% of GDP, compared to 40% in England.

This would be exacerbated by the impact of an ageing workforce, job losses in the financial services sector, and fewer jobs being created in the public sector.

PWC partner Mike Greig said: “Going forward, Scotland cannot afford the current level of public expenditure and we must find new ways to deliver more with less.

“Leaders who recognise the scale of spending squeeze that is coming are planning workforce reductions of 15% or more and up to 15% cuts in procurement spending.

“In addition they understand that they must urgently reform ways of working and transform service delivery.”

He went on: “Failing to take action now will lead to future draconian cuts across the board at a time when the public needs vital public services more than ever.

“The next three years will bring unprecedented expenditure pressure to the Scottish public sector and it is vital that we tackle this head on.

“A step change is required not only to balance the books and pay down public sector debt but also to ensure we make available resources to invest in the next wave of change and innovation to bring growth and prosperity to our country.”

A spokesman for Finance Secretary John Swinney said the report was “inaccurate” in its assessment of the size of Scotland’s public sector.

“There is no doubt that the UK is facing an extremely serious deficit in its public finances,” the spokesman said.

“The official figures for 2007/8 show that total public expenditure as a share of gross domestic product is 40% for Scotland, including a geographical share of North Sea resources in Scottish GDP, compared to a UK-wide figure of 41%.

“The Scottish Government is already taking action to respond to cuts imposed by Westminster.

“Our draft budget focuses on safeguarding effective delivery of frontline services and promoting economic recovery. And the Scottish Government is already delivering 2% cumulative efficiencies across the public sector each year and working to reduce the number of public bodies by 25%.

“The latest Government Expenditure & Revenue Scotland (GERS) report shows Scotland with a current budget surplus of £219 million, or 0.2% - compared with a UK deficit of £5.3 billion, or 0.4%. Full fiscal autonomy and independence are the key to a flourishing and economically successful Scotland.”