Mr McDonnell told interviewer Iain Dale a future Labour government would not stand in the way should the Scots want a second vote on their membership in the Union. He added any decision about holding a vote would be up to the Scottish Parliament. He said: “It will be for the Scottish Parliament and the Scottish people to decide that.
“They will take a view about whether they want another referendum. Nicola Sturgeon said by late next year or the beginning of 2021.
“We would not block something like that. We would let the Scottish people decide. That’s democracy.
“There are other views within the party but that’s our view.”
The comments come after Ms Sturgeon called for a “progressive alliance” with Jeremy Corbyn to stop Brexit.
The First Minister said she would do a deal with Labour leader to “lock the Tories out of government”.
She also did not rule out demanding a fresh independence referendum as the price of SNP support.
Though this has been ruled out by the Scottish Tories.
A spokesman said: “From top to bottom, Labour is incredibly weak on Scotland’s place in the UK.
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“We all know Nicola Sturgeon’s condition for support in Westminster would be green-lighting a second independence referendum.
“Now it seems John McDonnell is very happy to pay that price.”
The remarks by Labour were also attacked by Ian Murray, the party’s MP for Edinburgh.
He said: “These are utterly irresponsible comments from John McDonnell that betray our party’s values.