Former diplomat Lord Kerr said it was possible that MPs in the House of Commons could “duck the issue” when they get to vote on the UK’s eventual European exit deal later this year.
In these circumstances he insisted “Parliament won’t override a referendum without a referendum”, and would give the public another chance to vote on the matter.
Speaking about Brexit, the Lords’ crossbencher said the final terms of any deal with the rest of the European Union would not become known until late this autumn.
He said: “There will be a serious vote in Parliament in November or perhaps December.
“The options then would be buy the deal, don’t buy the deal and leave with no deal, ask for extra time to try to get a better deal, have an election, withdraw the Article 50 notification, or shall we ask the people.”
He insisted the “odds are shortening” on a so-called People’s Vote, saying: “I think there is a possibility that Parliament will duck the decision itself.
“I think Parliament would probably want to, having seen the terms, stay in the European Union, but it won’t decide to do that because I don’t think you can reverse a referendum decision except by a referendum decision.
“I think it is possible that is what Parliament may decide to do.”
He spoke out in a lecture on Brexit at Edinburgh University, where he described the act of leaving the EU as “self harming”, adding that the “best course would be to stop”.
Lord Kerr went on to say that the Brexit powers row between Westminster and Holyrood had left the UK “very close to a very serious constitutional crisis”.
MSPs in Edinburgh have voted against granting formal consent to the UK Government’s EU Withdrawal Bill - a move which could lead to the unprecedented situation of the UK pressing ahead with the legislation against the wishes of Scotland.
Lord Kerr said: “The Scottish Parliament has given legislative consent 170 times, and refused it only once before.
“When it refused it before, the Whitehall Government compromised and the Scottish Parliament did give legislative consent.
“This time I can’t see how the compromise comes about.”
He refused to predict how the ongoing dispute, over whether powers returning from Brussels should go to Edinburgh or London, would end up.
But he said the situation would be helped if the SNP had representatives in the House of Lords.
SNP policy is for the abolition of the Lords, but Lord Kerr argued that reforms going through the upper chamber would cut the number of Lords and also ensure its political composition was closer to that of the UK.
If those changes go through, he said the SNP would be “entitled to quota in the Lords, which if it doesn’t fill them will be unfilled”.
He added: “There will be empty seats in the Lords, empty seats that should be filled by Scots people representing Scotland and they won’t be filled because of SNP doctrine.”
Lord Kerr said: “My message to the Scottish Government is, it is time the SNP stopped being stuck on this arcane doctrine and got stuck in in Westminster.
“They do in the House of Commons, they are very well represented in the House of Commons.
“In the House of Lords they emulate Sinn Fein and refuse to be represented. Why? I don’t think it makes sense.”
He argued: “The theological objections in the SNP to the House of Lords are a bit out of date - the modern SNP, a party of government, should overcome these historical objections and get its representatives into the House of Lords influencing debate.
“They’re in the House of Commons, they make a very significant contribution to the House of Commons.
“I think Scotland would be better served, the House of Lords would be better served and the country as a whole would be better served if the Scottish Government had somebody there explaining what is their case.”