Britain's second biggest supermarket group Sainsbury's has warned that food could be left rotting at the border if supply chains are disrupted by customs checks once Britain leaves the European Union. 

Any new controls on imports and exports of food would increase costs and transport times.

This would make it harder to get fresh items to customers, the company's chief executive Mike Coupe said. 

"If you take our fresh produce supply chains, for example, we put things on a lorry in Spain and it will arrive in a distribution centre somewhere in England, and it won't have gone through any border checks," he said. 

This "has two effects: it adds cost, and it also has a detrimental effect on freshness - if you're shipping fresh produce from a long distance, even a few hours of delay can make a material impact," he said. 

Coupe said the retail industry would increasingly make its voice heard if the countdown to Brexit in March 2019 continued with no clear solution to the issue of customs controls. 

Industry body the British Retail Consortium warned last week that British shoppers could face higher prices and less choice unless Britain and the EU can agree how to handle issues such as border checks, haulage and food safety after Brexit. 

The opposition Labour Party has proposed keeping Britain in the single market and customs union for a transitional period after 2019 to avoid damaging jobs and the economy.