Theresa May’s deputy has insisted the Tories and Labour are making a “genuine attempt” to find a Brexit solution but warned compromises were needed from both sides.

Cabinet Office minister David Lidington said cross-party talks between negotiating teams had been “constructive” although they had yet to find an option which would attract majority support in the Commons.

Labour’s Emily Thornberry had raised concerns over the Government’s attempts to maintain an open border on the island of Ireland, and insisted the option of a customs union must be put on the table to deal with it.

Prime Minister’s Questions
Shadow foreign secretary Emily Thornberry, standing in for Jeremy Corbyn during Prime Minister’s Questions (PA)

The shadow foreign secretary also highlighted warnings from US House of Representatives speaker Nancy Pelosi that a US-UK trade agreement would not happen if Brexit undermined the open border, before claiming US president Donald Trump’s state visit risked being a “giant waste of taxpayers’ cash”.

Mr Lidington and Ms Thornberry deputised at Prime Minister’s Questions as Mrs May and Labour leader Jeremy Corbyn both travelled to Belfast for the funeral of murdered journalist Lyra McKee.

Ms Thornberry asked what the Government was doing “to bring her killers to justice” and said the incident and response from the “so-called New IRA” was a “sickening throwback”, adding those responsible want “to turn back the clock and destroy the progress that has been made” in Northern Ireland.

In her concluding remarks after exchanges on Brexit, Ms Thornberry said an open border was vital to preserving peace and security.

Prime Minister’s Questions
Cabinet Office minister David Lidington, standing in for Theresa May during Prime Minister’s Questions (PA)

She said: “If the Government is serious about putting the country first, the whole of our country, will the minister for the Cabinet Office accept that means finally getting serious about the cross-party negotiations and putting the option of a customs union on the table?”

Mr Lidington, in his reply, said: “The substance and the tone of those conversations between the Government team and the Opposition team have been constructive.

“I think there is a genuine attempt to try to find a way through but I’m not going to hide the fact that this is very difficult, because if it’s going to work it’ll mean both parties needing to make compromises and us ending up with a solution that unlike any other so far proposed will get a majority in the House.”

He listed proposals rejected by MPs, before adding: “It’s not just a matter for the Government or Opposition frontbenches, it’s a matter for every member of this House to take our responsibilities to the country seriously and find a way to agree on an outcome that enables us to deliver on the referendum result and to take this country forward.”

Earlier, Ms Thornberry criticised Mr Trump’s forthcoming state visit.

She said: “The Government is going to spend millions giving Donald Trump the red carpet, golden carriage treatment in June.

“And maybe the state banquet might even be worth it so as long as he’s forced to sit next to (schoolgirl climate activist) Greta Thunberg – or how about this, Greta on one side and David Attenborough on the other, that will be three hours well spent.

“But the truth is that it’ll all be a giant waste of taxpayers’ money because the US Congress will never agree to a trade deal unless we have a solution to the Irish border that will actually work, and this Government simply doesn’t have one.”

Mr Lidington replied: “It’s just two short years ago that (Ms Thornberry) said of President Trump ‘We should welcome the American president, we have to work with him’.

“I just wonder whether something has changed about the US administration or whether something has changed about her own leadership ambitions that causes her to alter her words in this way now.”

Tributes were also paid by both Mr Lidington and Ms Thornberry to those killed in the Sri Lanka terror attacks.