A European Union flag is waved in front of Big Ben and the Houses of Parliament in London, Britain, February 20, 2017. REUTERS/Toby Melville

LONDON (Reuters) - The British government needs to approach divorce talks with the European Union with more charm and less “cheap rhetoric” if it wants to get a good deal, former Conservative prime minister John Major said on Monday.

Prime Minister Theresa May, who plans to begin the formal process of leaving the EU by the end of next month, has said Britain will leave the bloc’s single market and instead seek a comprehensive free trade agreement post-Brexit.

Major, who campaigned to stay in the EU, said negotiations would require “statesmanship of a very high order”, but there was still little chance Britain would be able to match the advantages of the EU’s single market.

“It is much, so much easier to reach agreement with a friend than with a quarrelsome neighbor,” he said in a speech to the Chatham House international affairs think-tank.

“But behind the diplomatic civilities the atmosphere is already sour. A little more charm and a lot less cheap rhetoric would do much to protect the interests of the United Kingdom.”

Major’s own 1990-1997 premiership was plagued by disputes within his party over Europe, including Britain’s ignominious withdrawal from the European Exchange Rate Mechanism, the predecessor to the single currency, in 1992.

Major said there was a very high chance that Britain and the EU would not be able to reach an “acceptable” agreement within the two-year time frame set out under Article 50 of the EU’s Lisbon Treaty.

He urged ministers in May’s Conservative government to avoid raising Britons’ expectations unrealistically about the country’s prospects outside the EU.

Major also warned that post-Brexit Britain would become more dependent on the United States, and he described President Donald Trump as “less predictable, less reliable and less attuned to our free-market and socially liberal instincts than any of his predecessors”.