The factory has produced the official suits which Team GB athletes will wear to the Olympic Games in Rio this year.

Mr Johnson said house prices in the south of the country would fall if the UK votes to leave because of the reduced pressure of immigration on homes.

He said: "One of the things I could certainly imagine is that the pressure on prices, particularly in the south east, would abate.

"You'd get less pressure as a result of the huge influxes that we're seeing. There's no question at all that councils have to provide all sorts of services - there's huge pressure on the NS, there's huge pressure on school places, as a result of uncontrolled immigration.

"Housing is also a massive part of that. Councils have a duty to provide housing to people. I think you'd see a beneficial effect."

The former mayor also asked for a show of hands of people who are "apprehensive" about leaving the EU.

Around four of the forty employees put up their hands and Mr Johnson responded: "It'll be fine, it'll be fine.

"The great truth of this is we can and we are stronger and better if we take our own decisions and work on the basis of free trade."

During a tour of the factory Mr Johnson chatted to staff and managing director James Saunders, who has invited both campaigns to visit so that staff can make up their minds about the vote.

He delivered a scathing verdict on Mr Johnson's attire: "It's not what I'd have put him in,” said Mr Saunders.

“We have got some great Simon Jersey products available in the catalogue that he could select any number of formal suits form."

Kate McCann, Senior Political Correspondent