Vulnerable people would be put at risk in an independent Scotland because they would lose the safety net of a UK-wide welfare system, Coalition ministers have warned.

In its latest analysis paper on the impact of a Yes vote in September’s referendum, the Government claimed that spending on benefits per head of the population in Scotland is 2 per cent higher than in the UK as a whole – and has been as much as 9 per cent higher in the past. But the Scottish National Party dismissed the report as “scaremongering” and accused ministers of “hypocrisy”.

Meanwhile, the Scottish First Minister, Alex Salmond, said in a St George’s Day speech in Carlisle that an independent Scotland would look to build a high-speed rail link to the south. “Rather than paying our share of the borrowing costs for high-speed rail, as we wait decades for it to spread up from the South, we can use that money to build high-speed rail from the North instead,” he said.

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The Government analysis paper argues that the Scottish people enjoy “the best of both worlds”. Housing and skills policy are devolved so that local solutions can be found, while employment and social security remain with central government so that employers and job seekers can benefit from a UK-wide network of job centres.

Ministers warn it would cost a breakaway Scotland about £200m a year to provide this support for the unemployed. They threaten to ban an independent Scotland from “sharing” the UK’s benefits system if it wanted to have different policies, as the extra costs and risks “would not be in the interests of the Government”. If Scotland opted for its own system, the IT start-up costs alone would be between £300m and £400m, the report claims.

Iain Duncan Smith, the Tory Work and Pensions Secretary, said: “As part of the UK, Scottish people benefit from this resilient and unified system – which delivers the same support everywhere irrespective of peaks and troughs in economies of the nations or demographic differences.

“Proposals by the Scottish Government would risk the well-being of vulnerable people who are currently supported by this system.”

But Nicola Sturgeon, Scotland’s Deputy First Minister, said: “Welfare spending and pensions are more affordable in Scotland than the UK because they account for a smaller proportion of our tax revenues and national income.”