Thousands of pro-Europe protesters are marching on Parliament in a mass demonstration against Brexit.

Organisers predicted around 100,000 protesters would gather in central London's Parliament Square, where they were due to be addressed by Sir Bob Geldof and Liberal Democrat former cabinet minister Sir Ed Davey.

It forms part of a wave of protests dubbed the "autumn of discontent", with another anti-Brexit march scheduled to take place outside the Conservative conference in October.

The People's March For Europe carries the message “unite, rethink and reject Brexit” and organisers said leaving the EU “no longer holds credibility inside Westminster, let alone on the streets of Britain”.

The Government is at a crucial moment in the Brexit process as MPs are set to vote on the repeal bill, formally known as the EU (Withdrawal) Bill, on Monday for the first time.

Amid rising concerns about the progress of Brexit negotiations, Boris Johnson on Friday made a fresh attempt to push talks forward by suggesting Article 50 committed Brussels to discussing a future trading relationship with Britain at the same time as working through so-called Brexit “divorce” issues.

The Foreign Secretary intervened after senior European figures, including EU chief negotiator Michel Barnier, voiced scepticism that talks would move on to future trade relations by the previously planned date of October as negotiations so far have failed to deliver “decisive” progress.

The Government has been pushing to begin trade talks, arguing they are inseparable from the withdrawal issues which are currently being pored over by negotiators.

But the EU insists “sufficient progress” must be made on the divorce issues – a financial settlement, citizens' rights, and the Irish border – before trade talks can begin.

Arriving for an informal summit of EU foreign ministers in Tallinn, Estonia, Mr Johnson said Article 50 of the Lisbon Treaty, which provides the framework for the exit of a country from the bloc, states that the two sides should discuss future relations.

“Article 50 makes it very clear that the discussion about the exit for a country must be taken in context with discussion of the future arrangements, and that's what we are going to do,” the Foreign Secretary told reporters.

Meanwhile, an influential group of pro-Leave Tory MPs were coming under pressure from within the party and from Labour after signing a letter designed to pressure Theresa May into what is seen by some as a “hard” Brexit.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

The Prime Minister has been urged by Tory former minister Stephen Hammond to sack ministers and government aides on the Conservative European Research Group (ERG), which has circulated the letter.

And the revelation that the group receives public money prompted a group of Labour MPs to ask the expenses watchdog, the Independent Parliamentary Standards Authority (Ipsa), if the payments were within the rules.

Saturday's march received endorsement from Star Trek actor Patrick Stewart, who said the Leave campaign was based on the "huge falsehood" that leaving the bloc would release £350m of funding for the NHS.

“That £350m never existed," Mr Stewart. "The people of the UK were misled. Monthly reports are published on the economic impact of leaving the union – and they are all negative.”’