Vince Cable was accused of making the case for Scottish independence after it emerged he had planned to warn of the economic damage inflicted across the United Kingdom by the concentration of wealth in London and the South East of England.

He was set to raise the alarm in a speech in Glasgow tomorrow, according to a leaked draft of his remarks. The comments have now been dropped from its final version.

The Business Secretary had been due to say that the financial crisis of 2008 had turned the spotlight on the capital’s dominance over the entire British economy.

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In the early draft, Mr Cable adds: “Another result of the crash was to focus attention on the sectoral and regional imbalances within the UK economy, with financial services over-represented and London and the South East harming the prospects of other parts of the country through its sheer dominance.”

His comments have been amended for him to argue that the Government is working to tackle the disparity between London and other areas and is already bearing fruit in Glasgow.

The Scottish National Party, which obtained the leak, claimed the Liberal Democrat minister had inadvertently spelt out a key reason why Scots should vote Yes in September’s independence referendum.

Its treasury spokesman, Stuart Hosie, claimed the Business Secretary had “let the cat out of the bag”.

He said: “Vince Cable’s admission simply makes the economic case for independence, which would see decisions about Scotland’s economy made by the people who live and work here, rather than by a Westminster establishment fixated on London and South East England.”

Last year Mr Cable claimed that London “is becoming a giant suction machine draining the life out of the rest of the country”.

A Liberal Democrat source said the SNP had obtained an extract from an early version of the speech which had passed through various advisers’ hands before reaching Mr Cable.

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The deepening acrimony in the referendum battle was underlined when Alistair Darling, the leader of the Better Together campaign, compared First Minister Alex Salmond to the North Korean dictator Kim Jong-Il.

Mr Darling’s comments followed the surprise success of the UK Independence Party in Scotland in last month’s Euro-elections.

He said of Mr Salmond: “He said on the BBC that people voted Ukip in Scotland because English TV was being beamed into Scotland. This was a North Korean response. This is something that Kim Jong-Il would say.”

A spokesman for First Minister Alex Salmond said: “Alistair Darling demeans himself and his colleagues in the No campaign with these pathetic, puerile remarks for which he should now apologise.

“The debate on Scotland’s future is one that deserves far, far better than boorish and abusive personal insults, as do the people of Scotland.”