She will tell MPs that steps to sign trade deals with other countries and start enacting a new EU migration system can get going as soon as Britain leaves the bloc in March 2019.
The Prime Minister will seek to allay concerns the UK will be forced simply to languish as a helpless colony of Brussels for a two-year transition period because the EU wants its own rigid rules to apply throughout.
But hopes of securing a UK specific trade deal with Brussels were dented yesterday after EU chief negotiator Michel Barnier ruled it out.
He said: “They have to realise there won’t be any cherry-picking. They have to face the consequences of their own decision.”
He also claimed that negotiations on future relations would not start until the UK had left the bloc, although Britain expects the deal to be done and dusted by then.
A Government source said in response to Mr Barnier’s comments: “We are at the very early stages of the next phase of negotiations.
“We have a long climb ahead but the PM has been clear what the view looks like from the summit. She set out in her Florence speech our ambition for an ambitious and bespoke deal that delivers prosperity and security to every part of the UK.”
Mrs May today presides at a meeting of her Brexit “war cabinet” of leading ministers to discuss the next steps in talks, ahead of a full Cabinet meeting tomorrow.
In the Commons she will report back on last week’s summit of EU leaders which agreed talks had made sufficient progress to move to the next stage.
The breakthrough was seen as a major achievement for Mrs May and yesterday she said she was proving the doubters wrong.
She added: “In the face of those who want to talk Britain down, we are securing the best and most ambitious Brexit deal for our whole United Kingdom.”
But there are concerns over EU calls for Britain to stay bound by rules including free movement, European Court of Justice interference and a ban on trade deals with other countries during the transition.
Mrs May wants the EU to agree what she calls an “implementation period” of about two years after Brexit to help ease the UK into life outside the bloc.
She will tell MPs the EU and UK share a desire to make rapid progress on agreeing that handover period.
Yesterday Boris Johnson spelled out his demand that Britain must in the long term be free to break away from EU laws, not stay permanently and wholly aligned as some pro-Remain ministers would prefer.
Accepting permanent alignment with EU laws would consign Britain to being “a vassal state”, the Foreign Secretary warned. Sources insisted he was not at odds with Mrs May as she herself had made clear she will not agree a final deal that forced the UK to accept new EU rules while having little influence and no vote on them.
Mrs May is also likely today to repeat her pledges to protect and strengthen standards after Brexit in areas such as working practices and consumer and environmental safeguards.