May to keep Brussels waiting over Brexit talks announcement

But her official spokesman poured cold water over the rumours, telling reporters that the PM had always said she would trigger Article 50 by the end of March, and adding: "I've said 'end' many times but it would seem I didn't put it in capital letters strongly enough."

It is now thought that the most likely date for the historic move will be in the last week of March, following the special summit of the remaining 27 member states in Rome on March 25 to mark the 60th anniversary of the European Union.

The Prime Minister's European counterparts had been prepared for her to make an announcement this week, with April 6 pencilled in as the date for a meeting of the 27 other EU leaders to respond to the situation - a gathering which will now be pushed back until later that month.

The development came as Scottish First Minister Nicola Sturgeon announced plans to stage a second independence referendum before the expected date for UK withdrawal from the EU in spring 2019.

But the PM's spokesman insisted that the surprise announcement had not had a bearing on the timing of Article 50.

Notification on Tuesday would also have risked clashing with the general election on Wednesday in the Netherlands, where the anti-EU PVV party of Geert Wilders is challenging for a share in power.

The Prime Minister will only be able to fire the Brexit gun when the legislation allowing her to trigger Article 50 completes its passage through Parliament.

Brexit Secretary David Davis urged MPs to overturn changes to the European Union (Notification of Withdrawal) Bill introduced by the House of Lords, which would require Mrs May to guarantee the rights of EU citizens living in the UK and to give Parliament a "meaningful" vote on the deal she secures in the two-year negotiation.

Mr Davis told the House of Commons he was "disappointed" that the Lords had amended a Bill which passed through the lower House unchanged.

The majority of voters, regardless of whether they backed Leave or Remain, now wanted Mrs May to "get on with the job in hand and to do so with no strings attached", he said.

Mr Davis told MPs he felt a "moral responsibility" towards four million EU nationals in Britain and UK ex-pats resident on the continent and wanted swift agreement on their status.

And he said he hoped that a guarantee of their future rights would be confirmed in an exchange of letters in advance of the completion of the final deal, in order to end uncertainty for foreign nationals as quickly as possible.

He warned that the calls for a parliamentary vote on the deal could be interpreted as an attempt by MPs or peers to defy the will of the British people.

"Whilst it has been badged as a meaningful vote, the reality is there are some who would seek to use this to overturn the result of the referendum," he said.

"Any prospect that we might actually decide to remain in the European Union would only serve to encourage those on the other side to give us the worst possible deal in the hope we will do exactly that."

Urging MPs to reject the Lords proposals, he told the Commons: "These amendments will undermine the Government's position in the negotiations to get the best possible deal for Britain and that can't be in the national interest."

If the Commons overturns the Lords changes, the Bill gets sent back to the upper chamber in the latest stage of parliamentary "ping pong".

Peers are expected to back down in the face of opposition from the elected House, but some staunchly pro-EU members of the Lords could try to hold out.

Brexit activist Gina Miller, whose courtroom victory forced the Government to seek Parliament's approval to trigger Article 50, said she was "very disappointed" that MPs had failed to push harder for change.

Ms Miller told BBC Radio 4's PM: "As the saying goes, you can take a horse to water, but you can't make it drink. I think that's what has happened.

"My disappointment is that a number of MPs seem to think that their role is to be a rubber stamp, rather than to scrutinise and represent their communities on what's best for Britain. So I'm very disappointed in the lack of action from some MPs.

"Their role is to scrutinise the Government and they haven't asked enough questions, they haven't pushed for these amendments."

Ms Miller said she believed there had been "an awful lot of bullying" to prevent MPs from voting with their conscience on Article 50.

She confirmed that she was ready to go back to the courts if Parliament is not offered a meaningful vote on the final Brexit deal.