SENIOR Tories have warned Theresa May that the "monumental" problems with her Brexit plan cannot be solved by "cursory tweaks".

The Prime Minister is seeking changes to the backstop measure to prevent a hard border with Ireland but was told by former Cabinet ministers that may not be enough to win support in Westminster.

The ex-ministers - Remainer Nicky Morgan and Brexiteers Iain Duncan Smith and Owen Paterson - have been taking part in talks to find an alternative to the backstop following a Commons vote in favour of replacing the measure.

"The backstop in anything like its present form is simply never going to pass the Commons," they wrote.

Their intervention came after May held talks in Dublin with Taoiseach Leo Varadkar.

She was joined for the private dinner at official state guesthouse Farmleigh House by the UK's Brexit negotiator Olly Robbins and her chief of staff Gavin Barwell.

Varadkar stressed that no official negotiations would take place, but instead the meal presented an opportunity to "share perspectives" on Brexit.

Varadkar said: "I believe ultimately we are going to have to get this deal over the line and I am determined to do that."

Attorney General Geoffrey Cox held talks in Dublin with his Irish counterpart, Seamus Woulfe.

Cox has been leading work within Whitehall on providing either a time limit on the backstop or giving the UK an exit mechanism from it.

Both proposals have been rejected by Dublin, which insists the backstop cannot be time-limited if it is to provide an effective "insurance policy" against the return of a hard border between Northern Ireland and the Republic.

And the MPs involved in talks on the so-called Malthouse Compromise stressed that the Prime Minister had been instructed by the Commons to replace the backstop rather than merely seek changes to it.

In a newspaper article, Morgan, Duncan Smith and Paterson wrote: "It is almost as if the Prime Minister has forgotten the scale of the original Withdrawal Agreement's defeat (by 230 votes) or how unacceptable the backstop proposals remain to significant numbers of MPs on both sides of the House."

Meanwhile, Chris Grayling is facing calls to resign after a controversial no-deal Brexit ferry contract awarded to a firm with no ships was cancelled.

The Transport Secretary's decision to award Seaborne Freight a contract worth £13.8 million to run services between Ramsgate and Ostend had attracted widespread criticism.

The Department for Transport (DfT) said it had decided to terminate the contract after Irish company Arklow Shipping, which had backed Seaborne Freight, stepped away from the deal.

A DfT spokeswoman said: "Following the decision of Seaborne Freight's backer, Arklow Shipping, to step back from the deal, it became clear Seaborne would not reach its contractual requirements with the Government. We have therefore decided to terminate our agreement.

"The Government is already in advanced talks with a number of companies to secure additional freight capacity - including through the port of Ramsgate - in the event of a no-deal Brexit."

Labour seized on the situation to say Grayling should quit or be sacked.

Shadow transport secretary Andy McDonald said: "As we predicted, the Seaborne Freight contract has been cancelled.

"This cannot go without consequence. The Chris Grayling catalogue of calamities grows bigger by the day.

"This contract was never going to work but this Secretary of State, true to form, blunders from one disaster to another.

"Whilst Theresa May needs the few friends she has right now, we cannot have this incompetent Transport Secretary carry on heaping humiliation after humiliation on our country. He has to go."