AS polls show the Conservative Party has seen its lead in public opinion lose its bounce, the potential of a hung parliament increases the risk of the UK either crashing out of the European Union or facing a return to the “Brexit impasse horror show” of recent years, a polling expert has warned.

Professor Sir John Curtice, speaking at a hustings event hosted by The Herald in Glasgow, said the Tories’ lead in the poll had fallen back to 10 per cent – about the same level as it was when the election was first called.

But he said if their lead were to narrow further – say by six points – the probability of Boris Johnson winning a majority would be 50% compared to 50% for a hung parliament, he said.

“Because the Conservatives no longer have friends left in the House of Commons, if they don’t get a majority they will soon be in trouble,” he said.

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He outlined the case if opposition parties failed to achieve the votes to get the Tory government out – but Boris didn’t have the votes to get the withdrawal treaty through parliament. This would be a “narrow” range of 320-326 seats being won by the Tories.

“What happens in that situation, your guess is as good as mine,” he said.” Strictly speaking, we could just be heading for crashing out without a deal.”

Some Tory MPs who would back Boris’s deal with the European Union would, however, resist a sudden departure, he said, which would mean a return to the difficulties of parliamentarians having to decide how to handle Brexit.

“There’s that very narrow range of results which welcome back the Brexit impasse horror show,” he said.

Nevertheless, the SNP and the Liberal Democrats would be duty-bound to shore up a minority Labour government because they supported the General Election in hopes of achieving a second referendum, even if arguments remain over issues such as Trident and the unpopularity of Jeremy Corbyn as leader.

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He said: “The realpolitik of the situation here is if there is a majority of MPs from elected parties that are in favour of a second referendum then, although there are various noises about Trident and ‘we don’t like Jeremy Corbyn’, it would happen.

“Given the LibDems and SNP precipitated this election in order to precipitate a second referendum, it has to be the case that if there is a chance of sustaining a minority Labour administration in order to apply for an extension to article 50 and then put the issue to the electorate, they would”
But the Labour coalition would not last longer than a year, he predicted.

“My expectation would be if we were to have a deeply minority Labour administration put in for the purposes of having a second referendum, probably the three opposition parties could agree on a budget because they are on roughly the same page on spending and taxation.

"But I would think it would be unlikely that the government would survive roughly beyond this time next year. Because once Brexit is sorted one way or another the purpose of that government will have disappeared.

"We will all be back to the hustings again.”

On the outcome of a second referendum on Brexit, Mr Curtice said polls have been remarkably consistent with 52% in favour of overturning Brexit to remain and 48% still voting leave.

He added: “What that points to is that the ability of the remain side to mobilise that vote would be crucial, and there is no guarantee they would succeed in doing so.”

Professor Curtice was addressing an audience a hustings event arranged by the Association of Independent Professionals and the Self-Employed (IPSE) at the Radisson Blu hotel in Glasgow.