Shadow international trade secretary Barry Gardiner faced questions over whether he tells the truth in private or on television in a heated interview that has been labelled a "car crash".
Mr Gardiner was repeatedly asked about remarks he made to a private audience in which he said people were playing up the Irish border for political reasons, as he appeared on the BBC's Andrew Marr Show.
Host Emma Barnett quoted him as saying: "There are real economic reasons why people have played up the issue of the Irish border, and of course there are very good political reasons."
She asked the Labour MP: "Do you stand by that remark?"
Mr Gardiner - who served as a junior NIO minister in 2014 - replied: "There are reasons why people would wish to - if you look at the balance of trade and the importance of cross-border trade between the south and the north in Ireland it is extremely difficult to see how the Irish economy would withstand the imposition of cross-border controls."
Ms Barnett then pressed him, asking: "Do you stand by the remarks that people are playing up the Irish border for political reasons. You've said it? Which Barry Gardiner is the truth? The one that speaks in private or the one that is on television now?"
Mr Gardiner replied: "Sometimes you have conversations in private, and the reason they are held in private is because you can advance thinking and you can actually then try and, if all you ever do is stick by the given line, you'd never actually advance it because you'd never discuss anything with people - that's the reason for holding things in private.
"The important thing is that we in the Labour Party have come forward with the proposal - the Conservatives have not - which actually meets the problems of solving the Irish border and that is a new customs union which would minimise disruption on the border, and which would enable our jobs and our economy to be protected in this country because the supply chain across the border into Europe would not constantly be undermining our just in time supply chain."
The interview was branded a "total car crash" by Tory spokesperson Carrie Symonds.