THERESA May will warn Britain that an “unstable coalition of divisive Nationalists” could put Jeremy Corbyn in No 10 as a poll has pointed to a remarkable Tory revival and a Labour meltdown in Wales.

With opinion surveys suggesting Conservative fortunes are on the rise in Scotland, the latest Welsh Political Barometer poll by YouGov has pointed to the Tories winning a majority of parliamentary seats in Wales for the first time in the modern era.

After chairing a political Cabinet in Downing Street on Tuesday morning, the Prime Minister will travel to a range of seats in Wales and will speak at a campaign rally.

The poll of around 1,000 people conducted last week put the Conservatives on 40 per cent, up 12, Labour on 30 per cent, down three, Plaid Cymru unchanged on 13 points, the Liberal Democrats down one on eight and Ukip down seven on just six.

The snapshot suggests the Tories will finish with 21 seats, a gain of 10, winning such previous Labour strongholds as Alyn and Deeside, Bridgend, Cardiff South and Penarth, Cardiff West, Clwyd South, Delyn, Newport East, Newport West, Wrexham, and Ynys Mon.

Labour is forecast to finish with 15 seats, losing 10 overall while Plaid Cymru will retain its current three seats and the Lib Dems will hold onto its single seat.

"Wales is on the brink of an electoral earthquake,” declared Professor Roger Scully from Cardiff University.

“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," he said.

At the weekend, a poll gave the Tories in Scotland 33 per cent, suggesting Mrs May’s party could notch up as many as 12 seats north of the border.

Just 20 years ago in the Labour landslide of 1997, the Conservatives were wiped out in Scotland and Wales.

In her speech, the PM will warn that alliances between the Nationalists and Labour in the Welsh national assembly could provide a blueprint for similar coalitions in the rest of the UK, saying the Brexit referendum “should have been a wake-up call for a generation of politicians who have taken the people for granted for too long but, instead, those same politicians have closed ranks with Plaid propping up Labour in a direct example of collaboration we should expect in Westminster if Jeremy Corbyn and Leanne Wood get their way”.

In an article for The Western Mail, Mrs May writes that the June 8 election is a chance to “lock in” the economic progress Britain has made and to strengthen her hand in the Brexit negotiations with Brussels.

Referring to her Brexit plan, she says it is a plan to “regain control of our own money, our own laws and our own borders and to be free to strike trade deals with old friends and new partners all around the world”.

But she warns: “Yet Labour, Lib Dem and Nationalist opponents – Plaid Cymru here in Wales and Nicola Sturgeon’s SNP in Scotland – are already seeking to disrupt our negotiations even as 27 other European countries line up to oppose us. That approach can only mean one thing: uncertainty and instability, bringing grave risk to our growing economy with higher taxes, fewer jobs, more waste and more debt.”

She declares: “Every vote I receive will strengthen my hand as I negotiate with the prime ministers, presidents and chancellors of Europe. Every vote I receive will help me secure the best deal to strengthen our economy. Every vote I receive will be a vote to give me the mandate to deliver for Britain.”