Prime Minister Theresa May has been warned she faces a rebellion unless MPs are guaranteed a meaningful vote on the terms of the UK's withdrawal from the European Union. 

Rebel ringleader and former attorney general Dominic Grieve believes he has enough support to defeat the Government on Wednesday evening unless ministers give in. 

Labour is set to back Mr Grieve and urged would-be rebels not to be bought off by "warm words and woolly concessions". 

Mr Davis promised MPs there would be "a number of votes" on the final deal struck between the UK and EU. 

The Prime Minister's lack of a majority leaves her vulnerable to any Commons revolt and with up to 20 Tory MPs set to side with Mr Grieve in the division lobbies she could face a damaging blow to her authority. 

"I think there are quite a few who may support me - I think enough, if this comes to a vote, to defeat the Government," Mr Grieve told the BBC. 

Brexiteers reacted angrily to the threatened revolt, accusing the rebels of trying to "derail" the whole bill, which is needed to transpose EU legislation on to the UK statute book when Britain leaves in March 2019. 

Mr Grieve, who campaigned for Remain in the referendum, denied his amendment - which would require any final deal with the EU to be approved by a separate act of Parliament before it could be implemented - was designed to prevent Brexit happening. 

He said he tabled the change because without it the Government had the power to push the final deal through by the use of statutory instruments, denying MPs the vote they have already been promised by ministers on the outcome of the negotiations. 

Mr Davis was issuing a written ministerial statement clarifying his approach ahead of the Commons showdown, insisting that the withdrawal agreement would not be implemented until there had been a resolution passed by MPs and peers. 

The move appears to fall short of Mr Grieve's demand that the final deal is enshrined in a statute passed by Parliament before it can be put into effect. 

In his letter to MPs, Mr Davis specifically referred to Mr Grieve's attempt to rewrite the European Union (Withdrawal) Bill and said he was responding to concerns "by making clear that there will be a number of votes for Parliament on the final deal we strike with the EU". 

The EU's chief Brexit negotiator Michel Barnier wants the withdrawal deal finalised by October 2018 and the Government has committed to hold a vote in Parliament as soon as possible after the negotiations have concluded. 

In an attempt to address Mr Grieve's point about the power to use secondary legislation, Mr Davis said: "The Government will not implement any parts of the withdrawal agreement - for example by using Clause 9 of the European Union (Withdrawal) bill - until after this vote has taken place." 

In addition, he said the deal would have to go through the normal treaty ratification process and there would be primary legislation on the Brexit deal. 

"If Parliament supports the resolution to proceed with the withdrawal agreement and the terms for our future relationship, the Government will bring forward a Withdrawal Agreement and Implementation Bill to give the withdrawal agreement domestic legal effect. 

"The Bill will implement the terms of the withdrawal agreement in UK law as well as providing a further opportunity for parliamentary scrutiny."

"This legislation will be introduced before the UK exits the EU and the substantive provisions will only take effect from the moment of exit." 

Additional new laws may also be required to implement an agreement on the UK-EU relationship after Brexit, he added. 

Signalling support for Mr Grieve's amendment and a similar measure proposed by Labour, shadow Brexit minister Matthew Pennycook said: "Tory rebels have talked the talk, now they must walk the walk. 

"The decision MPs make today will determine whether or not the UK goes down the path of a Brexit that respects parliamentary democracy." 

While the Prime Minister seeks to avoid a parliamentary setback in Westminster, she may have one to contend with in Strasbourg where MEPs have hit out at the Brexit Secretary over his stance on the divorce deal agreed last week. 

Mr Davis's comment that the deal agreed by the Prime Minister and European Commission president Jean-Claude Juncker on the issues of citizens' rights, the Irish border and the UK's £39 billion divorce bill amounted to a "statement of intent" rather than a binding agreement has angered prominent MEPs. 

The European Parliament is set to vote on Wednesday on cross-party amendments tabled by Brexit co-ordinator Guy Verhofstadt, who warned that Mr Davis's comment risked "undermining good faith" established in the negotiations and calling on the UK to "fully respect" last week's deal. 

EU leaders are expected to agree on Friday that the Brexit talks can move on to the next phase, discussing a transition arrangement and the future relationship between the UK and the remaining 27 member states.