The EU and UK flags fly above the EU Commission offices in Westminster, London. Stefan Rousseau / PA Wire/Press Association Images LONDON — Five of the UK's leading business organisations are calling for the government to maintain access to the Single Market and Customs Union until a Brexit deal is reached and to prioritise the rights of EU citizens in the UK.

The heads of the British Chambers of Commerce (BCC), the Confederation of British Industry (CBI), manufacturing trade group the EEF, the Federation of Small Businesses (FSB), and the Institute of Directors (IoD) have all signed an open letter to the government.

The groups say they accept the result of last year's EU Referendum but have come together "to urge the Government to put the economy first." Collectively the groups speak for hundreds of thousands of businesses across the UK.

Business leaders are concerned about the government's stated position that "no deal is better than a bad deal" for Brexit. This could see UK businesses crash out of Europe in March 2019 with no clear rules on how to trade with the EU bloc.

Formal Brexit talks between UK and EU representatives begin on Monday. Chancellor Philip Hammond has dismissed the idea that the UK could stay in the Customs Union and Single Market following the UK's departure from the EU. He did, however, concede that no deal would be "very, very bad for Britain."

The business lobbies say in Monday's letter that a final Brexit deal should include tariff-free goods trade, minimal customs formalities at borders between the UK and the EU, and a "flexible system" of movement for both UK and EU workers "that enjoys public support."

The letter also stresses the importance of maintaining an "open and frictionless border" between Ireland and Northern Ireland throughout the transitionary period.

As well as business groups, the letter's signatories include Labour MP Keir Starmer. Starmer last week urged Brexit Minister David Davis to take a "new tone and approach" to Brexit talks and to rule out the idea that "no deal" would be better than a bad deal.

"The belligerent and reckless approach adopted by the Prime Minister to date has needlessly wrecked relations with the EU," he said. "A much more constructive and responsible tone is needed," he wrote, adding that "no deal has never been a viable option."