LONDON — From the purple-lit stage of a London ballroom on Monday, Prime Minister Theresa May of Britain pitched her draft deal for leaving the European Union to an audience of business leaders who, not long ago, hardly hid their distaste for the prime minister.

She had taken office two years ago complaining about corporate greed, threatening a crackdown on excessive pay and condemning free-market acolytes as “citizens of nowhere.” This summer, her then-foreign secretary, Boris Johnson, poisoned relations further when he wielded a four-letter expletive to tell businesses how little he cared for their interests.

But Mrs. May received a mostly warm reception on Monday — warmer than any she has gotten even from supposed allies in the five days since she unveiled her much-reviled plan to extract Britain from the European Union.

Her deal was, well, a deal, and it granted businesses some certainty.

That was enough for the business leaders sitting before her, though some urged the prime minister to soften proposed immigration restrictions after Britain’s split from the union.