Remainers have launched a campaign bus claiming the cost of quitting the European Union will be £2,000 million a week.
The staggering figure is based on analysis of leaked government reports predicting that all Brexit scenarios will significantly hit the economy.
Emblazoned with the slogan "is it worth it?", the bus will be touring the country.
It is a direct riposte to the Vote Leave campaign coach that suggested the NHS could be £350 million a week better off once Britain stopped contributing to EU coffers.
Liberal Democrat Tom Brake, one of the campaign supporters, said: "What this bus is about is reminding people of the lies that particularly Boris Johnson put across during the referendum campaign about how £350 million a week was going to be available to the NHS.
"Clearly it isn't. The point that is being made on the side of this red bus is that as a result of us leaving the European Union and the impact it will have on growth and the economy, the figures suggest the loss to the UK economy could be as high as £2,000 million a week. "
Asked why the public should believe the figure on the bus, Mr Brake said: "The reports commissioned by the Government have confirmed that, whichever model of trade deal the United Kingdom goes for, every single sector of the UK economy and every single region of the UK economy suffers financially.
"This is what their reports have stated is going to be the impact of Brexit."
Leaked documents EU Exit Analysis - Cross Whitehall Briefing - set out the impact of different scenarios after Britain leaves the bloc.
It suggested that, even with a comprehensive free-trade agreement with the EU, growth over the next 15 years would be 5% less than current forecasts.
Campaigners claim that works out to around a £2,000 million a week hit.
The Brexit Facts Bus is touring the UK for eight days and has been paid for through crowdfunding.
Charles Seaford, one of the organisers, said "These shocking leaked numbers show we would be £2,000 million a week poorer than we otherwise would.
"To put this in context, that is 80% of the NHS budget across the UK. These are not our numbers, they are the Government's numbers."