Time is fast running out to stop, suspend or even reverse Brexit before October when the withdrawal treaty is due to be finalised. One of the great myths of the Brexit debate since June 2016 is that there is a “final deal” which can be voted up or down.

Nothing is further from the truth. A formal withdrawal treaty is necessary when any country leaves an international treaty organisation – which, in essence, is what the EU is. There may be a declaration or statement of intent that accompanies the withdrawal treaty. Yet that will not be an over-arching final deal that defines the UK’s future relationship with the EU, landing somewhere between the full amputation desired by Liam Fox, Jacob Rees-Mogg and Nigel Farage, and what David Miliband called “the safe harbour” of the UK staying in the European Economic Area or rejoining the European Free Trade Association (Efta), and becoming a giant version of Norway.

Instead, there is agreement to keep talking and talking and hammering out thousands of mini-agreements, from creative industry access to preserving some possibility for the City to operate in Europe as it does today.

Thus a “Brexiternity” of negotiations could go into 2021 – and beyond, with Theresa May reportedly saying she would like these talks to continue until 2023, after the next election.

Michel Barnier told me he was not sure that continuation would be legally possible, as the decisions will be taken by the new group of EU leaders who are nominated to hold the top posts in Brussels for the next five-year EU governance term beginning in 2019.

In this period Britain loses all influence, as neither ministers nor officials who currently have a voice, a vote, and sometimes a veto on every EU decision will even be present, as the EU decides how to handle Britain in its new status as a “third country”. We will be supplicants like Canada, Japan or America – knocking on doors and hoping for a hearing.

What there won’t be in the near future is a final, definitive, black-or-white deal that can be voted on.

That is why Best for Britain, with all the George Soros money behind it, may be barking up the wrong tree in targeting individual MPs – the likes of Caroline Flint and John Mann – and pressing them to change their line on Brexit.

Labour MP Caroline Flint in 2015. Photograph: Roger Askew/Rex Features

Both those Labour MPs, like Gisela Stuart and Kate Hoey before them, have declared their position, and attempts to pressure them into changing their minds would have no more success than the leave campaign trying to persuade Antoinette Sandbach and other Tory MPs who are clear they cannot vote for anything guaranteed to make their constituents poorer.

Best for Britain is right to want to take the campaign away from London salons and the House of Lords, because the battle of Brexit will not be won in SW1 or SW3, let alone Notting Hill Gate or Holland Park.

If there is serious money to be spent to offset the massive amount of pro-hard Brexit propaganda from the offshore-owned press or – until recently – outfits such as the Legatum Institute, it should be spent on constituency audits that describe in clear language the direct consequences of Brexit for Barnsley, Bootle, Bath, Bassetlaw and beyond. These should be printed on Lidl-style brochures and put through letterboxes in homes across the country.

The consequences include: the closure of local horticulture firms as a new immigration bureaucracy stops the current easy hiring of workers; the loss of direct foreign investment, as companies seek countries without customs barriers and the prospect of losing European university funding; estate agents selling retirement homes in Spain no longer certain about the post-Brexit rights of British expats; European healthcare workers across the country feel uncertain and apprehensive about their future.

When the dire macroeconomic consequences are presented, such as the 90% drop in the flow of direct foreign investment to the UK, this may mean nothing to many voters. But give people a story about the effects on their town, on the firms they know, the hospital they trust, the university they are proud of, and opinions will shift.

Political Brexit takes place next spring unless Theresa May – and Jeremy Corbyn with her – decide to consult the people again. But full economic, social and cultural Brexit is not going to happen for a while yet – minds can still be changed. Trying to harass MPs in either direction is a waste of Soros money: Best for Britain and other campaigners need to take their argument directly to the people.

• Denis MacShane is the former Europe minister. His latest book is Brexit, No Exit. Why (in the end) Britain Won’t Leave Europe (IB Tauris)