The referendum is seen as an important test of public opinion in the mountainous central European nation, with Justice Minister Karin Keller-Suter having suggested a yes vote would be "worse than Brexit". However, Roger Koeppel, a politician with the Swiss People's Party (SVP), has said a yes vote is necessary to prevent Brussels turning his country into a "vassal state" in language highly reminiscent of UK Prime Minister Boris Johnson.

The pro-immigration SVP has the highest number of seats in the National Council, equivalent to Parliament in the UK, with Mr Koeppel one of its representatives.

The party is spearheading the push to take back control of immigration, echoing the phrase coined by Vote Leave campaign manager Dominic Cummings in the 2016 Brexit referendum.

However, a gfs.bern poll found 63 percent of respondents oppose the SVP proposal and 35 percent support it, suggesting voters want stability at a time of economic uncertainty during the coronavirus pandemic.

The SVP claims the current situation will increasingly result in young workers from outside the country supplanting older Swiss, with house prices being pushed up and schools and transport becoming overcrowded.

Opponents say the plan would rob business of skilled workers and torpedo accords which enhance non-EU member Switzerland's access to the EU single market.

A "guillotine clause" means ending free movement would also topple other bilateral pacts on land and air transport, procurement, technical barriers to trade, and research.

In the event that the nation backs the proposal, it will attempt to renegotiate the deal with the EU - although as Ms Suter has pointed out, Brussels could simply refuse to do so.

Citizens of the EU plus Iceland, Norway and Liechtenstein, which with Switzerland are members of the European Free Trade Association (EFTA), made up 68 percent of the 2.1 million resident foreigners in 2019. More than 450,000 Swiss live in the EU.

Should the referendum drive, as expected, fail, the government will turn to its biggest foreign policy problem: a stalled treaty which would cement ties with the EU but which critics say infringes too much on Swiss sovereignty.

Speaking to Express.co.uk earlier this month, Mr Koeppel said: "The reason that I went into politics was because it was so embarrassing and so annoying how the EU behaves towards Switzerland, I decided it was not enough to write against this, I had to really participate.

"I think my perception was a feeling of annoyance towards the European Union, which is so domineering.