Theresa May is trying to play down the Tories' double-digit poll lead over Labour

Theresa May deliberately cast doubt over opinion polls that give Conservatives a double-digit lead over Labour on a visit to Wales on 25 April.

The prime minister, citing Plaid Cymru's alliance with Labour in the Welsh national assembly, warned supporters that Jeremy Corbyn could still form a "coalition of chaos" with the SNP after 8 June.

"Make no mistake, it could happen," she said. "Remember the opinion polls were wrong in 2015 general election? They were wrong in the referendum last year. And Jeremy Corbyn himself has said that he was a 200/1 outsider for the Labour leadership in 2015 and look where that one went.

"So we must not be complacent, I'm not complacent. I'm going to be out and about, I'm going to be campaigning and working for every single vote."

The comments come just a day after a poll from YouGov for Cardiff University, of more than 1,000 Welsh voters between 19 and 21 April, put the Tories on 40% (+12) and Labour on 30 (-3).

The survey suggested that the Conservatives could win the most Welsh parliamentary seats for the first time in 100 years.

"Something extraordinary could be about to happen," said Cardiff University's Professor Roger Scully.

"Wales is on the brink of an electoral earthquake. The Conservatives appear to be on course to win the majority of Welsh parliamentary seats for the first time in the democratic era, while Labour faces losing a general election in Wales for the first time since 1918."

UK-wide national opinion polls have also put the Tories well in front of Labour. The latest survey from ICM, of more than 2,000 voters between 21 and 24 April, gave the Conservatives a 21-point lead (48% versus 27%).

Polling analyst Matt Singh, the founder of Number Cruncher Politics, told IBTimes UK that predicted landslides tend to depress turnout at general elections.

"In terms of the picture of the polls and how that might affect turnout and people's assumptions about the result, it is a very similar situation to what we had two decades ago when Tony Blair and Labour were widely expected to win by a landslide [at the 1997 general election]," he said.

"They were very keen to push home the message, as the Conservatives are now, about not being complacent and not trusting the polls.

"Because, then as now, the polls had got the previous election horrendously wrong. On that occasion it worked. Whether it will work this time remains to be seen.

"Any time you get a predicted landslide it does tend to depress turnout to some extent. So it will be interesting to see if that happens and how it happens. It depends who stays home, which is really what is going to determine the election."