By MARK MCLAUGHLIN

A SURGE in Labour support could dent Theresa May’s hopes of a hard Brexit mandate and Nicola Sturgeon’s desire for a second independence referendum.

A clutch of new polls have shown the Conservative lead over Labour shrinking throughout the UK, including one which put Theresa May's party just six points clear.

Meanwhile, a shock survey of Scottish voters suggests the SNP’s ranks at Westminster could be more than halved.

Support for the SNP has fallen to 39 percent meaning they could be heading for victory in just 24 seats — down from 56 in their barnstorming 2015 landslide, the survey suggests.

While the SNP would remain the biggest Scottish party at Westminster, a decline of this magnitude would be seized upon by their opponents as evidence that their plan for a second independence referendum is faltering.

The Tories would be the biggest beneficiaries of the SNP retreat, with the support of 29 percent of voters translating to 17 seats, but Labour is gaining ground with 25 percent of the vote and potentially a dozen seats.

The views of nearly 2,000 Scots was gathered by SurveyMonkey, which is not a member of the British Polling Council but its prediction of a partial Labour recovery echoes UK-wide polls conducted by more established firms.

Theresa May called the snap general election on June 8 with an appeal to make her strong as she heads into Brexit negotiations by evicting Europhile MPs calling for continued single market membership, a second Brexit referendum or "half in, half out" deals in Scotland.

But John Curtice, Britain’s leading polling expert, said some polls suggest the Tories “really are in trouble” on June 8.

He said: "The clear, consistent message from the polls is that the Conservative lead has narrowed.

“Why does this matter? It matters because we are now in a position where the leads are such that the Conservatives can no longer be sure of getting the landslide majority that they want.

“Some pollsters are suggesting that they really are in trouble and that it is getting rather close, others suggest that it is further apart.”

An ORB poll for the Sunday Telegraph had Tories down two points in the past week on 44%, six points ahead of Jeremy Corbyn's Labour on 38% (up four points).

The 38% score equals Labour's best rating since Mr Corbyn became leader and would see him comfortably outpoll Ed Miliband and Gordon Brown's election results.

In the Sunday Times, a YouGov poll put Tories seven points ahead on 43% (unchanged since a similar poll on Friday), with Labour down two points on 36%.

An Opinium poll for The Observer found the Tory advantage had fallen from 13 to 10 points over the past week, with Theresa May's party on 45% (down one point), with Labour on 35% (up two).

And a ComRes survey for the Sunday Mirror and Independent showed the gap between the parties narrowing from 18 to 12 points over the past fortnight, with Tories on 46% (down two), Labour on 34% (up four).

Although the results are less dramatic than Friday's YouGov survey, which found the Conservative advantage squeezed to just five points, they tally with the trend in a number of polls which have shown Labour gaining on the Tories after having begun the election race as much as 25 points adrift.

All the surveys were conducted after Monday's suicide bomb in Manchester.

The ComRes poll found Mrs May was rated best leader to keep Britain safe from terrorism, by a margin of 42% to 16% for Mr Corbyn.

But her ratings on this and almost every other measure had declined over the fortnight since the questions were last asked, while the Labour leader's had improved.

Labour was preferred by a margin of 42% to 37% for having the "best policies for people like me and my family". But 51% said that Mrs May would make a better PM, compared with 30% for Mr Corbyn.

The Prime Minister was seen as best choice to represent Britain on the world stage, lead negotiations on Brexit and reduce net migration, while Mr Corbyn was rated best to improve the NHS, look after the interests of hard-working families and protect older people.

The ORB poll suggested a shift towards Mr Corbyn among women over the course of the campaign, with the proportion saying they would vote Labour rising from 31% to 40% since mid-May.

The Opinium poll found Mrs May's approval ratings had slumped from plus-17 to plus-11 over the week, while Mr Corbyn's rose from minus-18 to minus-11.

An ICM poll for the Sun on Sunday put the Tories on 46%, a 14-point lead over Labour on 32%.