Britain's luxury sector, including names such as fashion house Burberry and car maker Bentley, could lose up to 6.8 billion pounds in exports a year if the world's fifth largest economy crashes out of the European Union without a deal, research commissioned by the sector indicated.

The United Kingdom's tortuous crisis over EU membership is approaching its finale with an extraordinary array of options including a delay, a last-minute deal, a no-deal Brexit, a snap election or even another referendum.

Research commissioned by Walpole, the lobby group for the luxury industry, indicated that up to a fifth of British luxury exports would be at risk if the United Kingdom left without a deal on March 29. Reuters saw excerpts of the research.

"British luxury businesses are committed to staying in Britain, but we are losing patience with the government taking us to the knife edge of no-deal," said Helen Brocklebank, the CEO of Walpole.

"The cost to the UK economy in lost exports from British luxury will be nearly 7 billion pounds and we believe that money should be used to strengthen the country not diminish it. We urge the government categorically to rule out no-deal exit."

Walpole's counts 250 luxury brands amongst its membership, including Alexander McQueen, Burberry, Bentley, Claridge's, Dunhill, Harrods, Glenmorangie, Net-A-Porter, Rolls-Royce Motor Cars and Wedgwood.

The bulk of the damage would be due to changes to market access driven by tariff and non-tariff measures, for example, regulations such as health and safety requirements or environmental standards, according to the research.

About 80 percent of Britain's luxury goods go overseas, and Europe is its largest market.

Prime Minister Theresa May was scrambling on Monday to clinch concessions from the European Union in a last-ditch attempt to avoid another humiliating defeat in parliament of her deal to exit the bloc.

May has offered lawmakers the vote on Tuesday on what she had hoped would be a revised deal.

If her deal is defeated, May has said she will give lawmakers a vote on Wednesday on leaving without a deal on March 29. If they reject that, then they will vote on Thursday on delaying Brexit.