The leaked document says 18 EU states carry out more physical inspections of goods than Britain does

Extra customs checks could push up the cost of imported goods even if Britain signs a free trade deal with the EU, according to a leaked government document.

Senior officials at HM Revenue & Customs warned that prices could rise by as much as 24%, while UK exports risked being subjected to “burdensome procedures” at EU ports.

As Theresa May prepares to trigger article 50 on Wednesday, she has made it clear that Britain will not remain a full member of the EU’s customs union after Brexit. Instead, the government will try to strike an agreement to ensure trade with the Continent remains as “frictionless” as possible.

However, the leaked document states that a free trade deal like the recent EU-Canada agreement would leave goods