Former Prime Minister John Major lambasted Britain's preparations for leaving the European Union on Monday, saying the government must offer more charm and less "cheap rhetoric" if it wants to get a good deal.

Major, who led the U.K.'s Conservative government between 1990 and 1997, accused pro-Brexit politicians of giving Britons unrealistic expectations of life outside the EU.

Prime Minister Theresa May — like Major, a Conservative — plans to invoke Article 50 of the EU's key treaty, triggering two years of exit talks, by the end of March.

Major said the government's goal of settling divorce terms and forging a new relationship with the bloc within two years is "very, very optimistic."

In a speech at the Chatham House think tank that he billed as a "reality check," Major said voters must be given a better idea of "the timescale and complexity of the huge undertaking that lies ahead."

He said there is a "real risk" that the U.K. will not get the close free-trade deal with the EU that the government is seeking.

"Behind the diplomatic civilities, the atmosphere is already sour," Major said. "A little more charm, and a lot less cheap rhetoric, would do much to protect the U.K.'s interests."

Major, who backed the losing "remain" side in last year's EU membership referendum, said victorious "leave" campaigners should stop telling their opponents to quietly accept the result.

He said the 48 percent who voted to stay in the EU "care no less for our country than the 52 percent who voted to leave."

"It is not 'arrogant' or 'brazen' or 'elitist' or remotely 'delusional' to express concern about our future after Brexit," Major said. "Nor, by doing so, is this group undermining the will of the people: they are the people."

He also cautioned that leaving the 28-nation bloc would weaken Britain's voice in the world and make the U.K. more reliant on the United States and new President Donald Trump — "a president less predictable, less reliable and less attuned to our free market and socially liberal instincts than any of his predecessors."

In response, May's office said the government "a clear plan to get the best deal for the United Kingdom and are going to get on with the job of delivering it."