THERESA May is facing the prospect of the House of Lords blocking the UK Government's Brexit Bill if Holyrood continues to oppose the flagship legislation.

As the EU Withdrawal Bill successfully passed through the House of Commons and will now be debated in the upper chamber from the end of this month, Labour’s Lord Foulkes said if MSPs refused to give their consent, then "one of the possible options" was that the unelected chamber could try to stop the legislation in its tracks.

“People say the House of Lords has no legitimacy but if there is no Legislative Consent Motion, then we could say we would be doing what the Scottish Parliament wants us to do.”

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Asked what would happen if the Lords succeeded in blocking the bill in those circumstances, the former Scotland Office Minister replied: “We would be in unchartered waters.”

Liberal Democrat peer Lord Campbell said it was “not impossible” that the Lords could attempt to block the legislation if MSPs withheld their consent. “An attempt could be made but I would not bet the farm on it being successful.”

The former party leader said there might be a deal of sympathy among peers for Holyrood’s position but stressed this was a UKwide piece of legislation and the elected chamber’s view would hold sway. “This is a UK House of Lords,” he added.

Today, conveners and their deputies from three influential committees in the Scottish Parliament are due to travel to Westminster for a meeting with their counterparts in the Lords - where the SNP has no representation - to air their concerns about the fact that UK ministers failed to honour their promise and amend the legislation during its passage through the elected House. It will now be amended in the Lords.

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Last week in a unanimous report from Holyrood’s Finance and Constitution Committee, MSPs made clear legislative consent for the bill, which transfers European law into UK law, would not be given unless Clause 11, which deals with devolution, was replaced or removed.

The SNP’s Bruce Crawford, the committee chairman, said: “If a constitutional crisis is to be averted, it is vital that the UK Government brings forward changes to the bill that properly respect the devolution settlement.

“All three of our committees welcome this chance to share our concerns with the Lords and appreciate their willingness to engage on issues that potentially endanger the devolution settlement,” he added.

The Herald was told the MSPs, who represent the SNP, the Conservatives and Labour, hope to meet the chairmen of the Lords EU and Constitution, Lord Boswell and Baroness Taylor respectively, as well as some MPs.

Anger and dismay have been expressed at the Conservative Government’s failure to amend the legislation in the Commons to allay fears of a “power-grab” and to reaffirm the principles of the devolved settlement.

During the Report Stage on Tuesday night, Stephen Kerr, the Tory MP for Stirling, expressed his exasperation, telling MPs: “It sticks in my craw to think unelected Lords will make the vital amendments to this vital constitutional Bill.

“It is not really good enough and as a Member of the House of Commons I hang my head to think we have somehow dropped the ball."

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Yesterday, Ian Blackford, the SNP leader at Westminster criticised the Government for its "breach of faith" over the bill, saying it was a "democratic insult" that Theresa May now had to "rely on Lords to dig her Government out of a hole”.

Last night, MPs approved the legislation by 324 votes to 295, a majority of 29, with the Government seeing off a series of proposed amendments during a marathon two-hour voting period.

In one vote, on keeping Britain in the European single market, which was supported by the Nationalists, the Greens and the Liberal Democrats, while Labour's frontbench abstained nearly 50 of the party's MPs, including Edinburgh MP Ian Murray, defied Jeremy Corbyn and backed the amendment, which was defeated. Three Labour MPs also defied their leader by voting with the Government against the amendment.

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After the bill was given a Third Reading, David Davis, the Brexit Secretary, said it was essential for "preparing the country for the historic milestone" of leaving the EU.