PM's 'deal or no deal' Saturday showdown faces wrecking attempt

LONDON (Reuters) - British Prime Minister Boris Johnson will have to fend off an attempt to wreck his "deal or no-deal" Brexit vote on Saturday, as a group of lawmakers propose to delay giving parliament's backing for his new exit agreement.

Johnson confounded his opponents on Thursday by clinching a new deal with the EU, even though the bloc had promised it would never reopen a treaty it agreed last year.

But that was only half the challenge.

He now has to persuade parliament, where he does not have a majority, to back the deal, and has convened the country's first Saturday sitting in 37 years in order to do so.

That vote could be in doubt because expelled Conservative lawmaker, Oliver Letwin, has proposed that the decision to back a deal or not be deferred until separate legislation to implement the terms of the deal has passed through parliament.

This proposal, known as an amendment, will be put to a vote at the end of Saturday's debate if selected by Speaker John Bercow.

If the amendment is approved by parliament, Johnson's deal would not then be put to a vote on Saturday.

The amendment has the support of members from several different parties, some of whom want to delay Brexit.

The law states that if Johnson has not secured approval for his deal by Saturday, he must write to the EU requesting a delay to Brexit until Jan. 31 2020.

The move by Letwin, who says he supports the deal, is seen as an attempt to close a loophole whereby Britain could end up leaving the EU without a deal if one is approved on Saturday, but the legislation to implement it is blocked or delayed.

Letwin was among 21 lawmakers expelled from the Conservative Party last month after they rebelled against Johnson in a bid to prevent a no-deal Brexit.

He said: "My aim is to ensure that Boris’s deal succeeds, but that we have an insurance policy which prevents the UK from crashing out on 31 October by mistake if something goes wrong during the passage of the implementing legislation."

The Letwin amendment would not completely crush Johnson's hopes of leaving on Oct. 31. If he can get the necessary implementation legislation through parliament in time - which he says he can, but others see as a stretch - then Britain could still leave on schedule.

The opposition Labour Party has not said whether it will support the amendment, but doing so would be consistent with their opposition to Johnson's exit deal. The Scottish National Party said they would probably back the amendment.

(Reporting by William James; editing by Stephen Addison)