Britain’s income will be boosted by £20bn through concluded and future international trade deals that have been brokered by the European Union, according to the business department.

In a written Parliamentary question, Labour MP Emma Reynolds asked what the benefit had been to the UK economy of preferential trade agreements the EU has negotiated with countries outside the bloc.

Business Minister Anna Soubry replied: “The cumulative impact of all concluded, ongoing and potential trade negotiations currently being undertaken by the EU could boost UK GDP by over £20bn in the long run.”

The figure is a fillip to the Britain Stronger in Europe campaign, which is promoting an In vote to settle the UK’s future EU membership. With the referendum due by 2017, recent polls suggest the In and Out campaigns are running a statistical dead heat.

The two “Brexit” groups, Vote Leave and Leave.EU, believe Britain could organise superior trade deals with other countries and trading areas if it left the bloc. But the Parliamentary answer suggests the UK has benefited from deals negotiated centrally by Brussels, and would miss out if it left the EU. Ms Reynolds, a Europhile who was shadow communities and local government secretary until Jeremy Corbyn became Labour leader last month, told The Independent: “The UK’s membership of the EU gives us access to other markets around the world on better terms than we could negotiate if we go it alone.

“The EU single market has 500 million consumers. This gives us a powerful hand in trade negotiations with big economies such as those of the US, India and Japan. Opening up access to these markets will bring huge opportunities for British businesses and boost inward investment and job creation.”