Support for Scottish independence is at 39 per cent, while opposition has fallen four points to 42 per cent, according a poll published yesterday.

The ICM survey for the Scotland on Sunday newspaper revealed the highest level of support for a Yes vote since last August.

Excluding people who have not yet made up their minds, the results put Yes on 48 per cent and No on 52 per cent, leading the Yes Scotland campaign to claim it is “confident” of securing the necessary two-point swing on 18 September.

Yes Scotland chief executive Blair Jenkins said: “The extreme negativity of the No campaign is proving a major turn-off for voters, and month-by-month they are paying the price.”

Better Together campaign director Blair MacDougall said the poll was “a reminder that there can be no complacency” but reiterated that the poll was “just the latest to show a majority of Scots want to remain in the UK.”

Polling experts agree that although No remains in the lead, the gap with Yes appear to have been tightening over the past few weeks.

Professor John Curtice of Strathclyde University said that the ICM survey was the “closest seen so far” in the referendum campaign.

“This is another poll showing the No side is in a real battle if it wants to keep Scotland in the union.

“When the ‘don’t knows’ are excluded, it is the highest Yes vote in a poll that has not been commissioned by a partisan organisation.”