Labour's McDonnell under fire over Northern Ireland customs union view
The DUP has slammed the shadow chancellor after he said a customs union between Northern Ireland and the Republic must survive Brexit for the good of the economy.
DUP deputy leader Nigel Dodds claimed John McDonnell's "pro-united Ireland mask has slipped once again".
The Labour MP had said that "discussions should be had" about preserving an open union between the North and the South after the UK's exit from the EU.
Mr McDonnell, speaking on the BBC's Andrew Marr Show, said: "Bringing back a hard border I think would be a nightmare, I think it would not be practical anyway. We have to have a relationship which is as close to the customs union.
"I would not want to see anything that undermines the peace process in particular and all the gains that we have had."
He added: "We are not saying the customs union, we're saying a customs union and that's a discussion that should be had."
When pushed on whether there should be a "unique arrangement" over a customs union between the North and the South, he said: "I think that's part of the discussions that need to take place."
But Mr Dodds said: "John McDonnell has always wanted a united Ireland therefore it is no surprise he wants to build a new border in the Irish Sea as the United Kingdom exits the EU."
The DUP MP said there would be "no new borders erected in the Irish Sea".
"John McDonnell and others have sought to use 'threats to the peace process' as a bargaining chip by asserting Brexit will mean armed checkpoints. McDonnell should remember that the watch towers existed for security reasons rather than customs purposes," he added.