A shock poll has given the Yes camp the lead in the Scottish referendum battle for the first time, amid signs of infighting among senior figures backing the union.

The YouGov research for the Sunday Times found yesterday that 51 per cent supported independence, compared to 49 per cent who wanted to remain in the UK.

The results are the latest evidence of a dramatic surge for the campaign headed by First Minister Alex Salmond, which has seen the gap between the sides – once regularly in double digits – vanish in a matter of months.

The two point gap is within the margin of error for such polls, meaning the contest, which climaxes on September 18 is effectively too close to call.

Rumours about the latest YouGov findings have been swirling for days. The firm has charted a remarkable turnaround for Yes, which has seen them recover from a 22 point deficit in just one month.

Writing in the Sunday Mirror, former Prime Minister Gordon Brown acknowledged that the referendum battle was proving tougher than some had expected – and laid the blame squarely on the Tories.

“Why has it been difficult to win Scottish votes in support of this principle of sharing that most Scots hold dear?” the Labour MP for Kirkcaldy and Cowdenbeath wrote.

“Many are angry that the Bedroom Tax was imposed upon Scots against their will while at the same time the very wealthy received tax cuts. The SNP also claim that the ramifications of any Tory privatisation of the NHS in England will cut budgets in Scotland. But English and Welsh people have already given an answer to the SNP claims. The answer is that 90 per cent of English people want to keep the NHS public and retain it free at the point of need.

And the vast majority across the whole UK dislike the Bedroom Tax and would even consider more taxes to make our NHS better.”

He added: “Our union is not out of date or an anachronism or a museum piece but a unique, unparalleled, multinational living partnership that Europe and America cannot match or mirror.

“And what our ancestors built up, no nationalist should be allowed to split asunder.”

The poll shows a four point increase in support for Yes from the last YouGov poll published earlier this week. The No camp were leading by 14 points in mid-August and 22 points early last month, when undecided voters were excluded.

Alistair Darling, leader of the pro-Union Better Together campaign, said the poll “must now serve as a wake-up call to anyone who thought the referendum result was a foregone conclusion”

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