Merseyside and Manchester metro mayor candidates Andy Burnham and Steve Rotheram have challenged the Prime Minister to hold true to her promise to close the North-South divide.

The two MPS are demanding Theresa May "ends a summer of damaging speculation over the future of the Northern Powerhouse."

In a letter to Mrs May the Labour mayoral candidates said promised investment in rail infrastructure was essential if the Conservative Party was to deliver on its pledges to people in the North.

The 2015 Tory manifesto promised investment in modern rail links across the North and a new "HS3" scheme.

However, say the pair, during August repeated briefings by Government sources said the Prime Minister planned to pull the plug on the Northern Powerhouse and "curtail HS3."

The MPs called on Mrs May to use the autumn statement in the Commons to make a clear commitment to the most ambitious version of a HS3 scheme linking Liverpool with Manchester - including the airport - and on to Leeds and other northern cities.

Mr Burnham, MP for Leigh, said: "Before the last election you couldn't escape Tory MPs touring the North and promising the earth.

"But now they are changing their tune.

"If Theresa May confirms the reports and pulls the plug on the Northern Powerhouse, it will be the biggest betrayal of people here since Margaret Thatcher pulled the plug on our industries in the 1980s.

"The vote in the recent Referendum reflected a deep feeling of abandonment in many Northern communities by the political elite.

"The right response to Brexit is to deepen the commitment to the Northern Powerhouse, not abandon it.

"We are still prepared to give the new Prime Minister the benefit of the doubt and stand ready to work constructively with her, as we have in the past, to help her deliver her welcome commitment to close the North-South divide."

Mr Rotheram, who represents Walton, said: “I have long been sceptical of some of the promises made by both the Tory and Coalition Governments relating to the rebalancing of the economy.

"Now it looks like my fears have been realised as Theresa May appears to be rowing back on plans for targeted economic interventions.

"It looks like the Northern Powerhouse could go the same way as the Big Society - a clever vote-seeking sound-bite consigned to the political dustbin of history.

"The new metro mayors need the government to support their work, not hinder their progress with lacklustre support and uncertainty.

"That is why today we are calling on the Prime Minister to fulfil the promises her party made to the people in the North West.”

The full letter to Theresa May says:

Dear Prime Minister,

We understand that the Cabinet met yesterday to discuss the UK Government's detailed plan in response to the outcome of the EU Referendum.

As we feel sure you will agree, the vote in June indicated more than a concern with our membership of the EU.

We believe it reflected a much deeper sense of abandonment felt in many former industrial communities, particularly across the North.

With this in mind, we have become increasingly concerned at the growing suggestions coming out of your Government over the summer about the future of the Northern Powerhouse concept.

In early August, the Times reported that you are poised to scrap it and instead "shift the focus to other rural and industrial areas".

It went on to say that you are planning to impose greater cost controls on HS2 and "could curtail HS3".

Worryingly, the same newspaper last week repeated similar suggestions.

We find these words very surprising as we both recall vividly the very welcome commitment you made on entering office to close the North-South divide.

We believe that scrapping the Northern Powerhouse would not just contradict your own words, it would also be entirely the wrong response to Brexit.

If anything, the Government should now be deepening its commitment to it, not abandoning it.

But, perhaps most importantly, it also would be a serious breach of the manifesto on which you were elected just over a year ago.

As you will recall, one of the flagship promises in that manifesto was a commitment to "rebalance our economy and build a Northern Powerhouse".

It went on: "By connecting up the North with modern transport links, we will enable its great cities and towns to pool their strengths ... build High Speed 2 and develop High Speed 3 to join up the North".

These pledges were particularly significant to people here. They have put up with poor rail services for far too long.

Rail services from East to West across the North are completely inadequate and lag far behind the Midlands and the South East.

Consequently, the motorways across the North of England are at full capacity. This is not sustainable.

Far from powering on, the economy of the North of England risks grinding to a halt if a plan is not put forward to deliver those promised modern transport links.

We believe that investing in modern rail links across the North of England is the single highest investment priority for transport in our country and that delivering an HS3 scheme (also referred to as Trans-Rail North) is even more important than HS2.

In truth, both are needed if the country is to develop a modern integrated transport system.

That is why we are seriously concerned by the suggestion that cost-cutting on HS2 could lead to the curtailment of HS3. There can be no Northern Powerhouse without major investment in transport.

We fully understand that there are other pressing issues in your in-tray at the moment.

But we also hope you will appreciate how, after all the promises people in the North have been given by the Conservative Party, they are feeling uncertain as to where exactly they stand in relation to the intentions of your Government.

Our purpose in writing to you ahead of the new political season is to ask you to clear up this uncertainty at your earliest convenience, most notably in your Party conference speech and in the Government's Autumn Statement. In particular, we make two specific requests:

First, that you clarify your plans for further devolution in England and restate your personal commitment to delivering the manifesto commitment to "build a Northern Powerhouse";

Second, in the Autumn Statement, you make a clear commitment to the most ambitious version of a High Speed 3 scheme, linking Liverpool with Manchester (including the airport) and onwards to Leeds and the other cities of the North.

As ever, we stand ready to work with you constructively, as we have in the past, and in particular to help you deliver on your important promise to close the North-South divide.