May is seeking to drum up support for her agreement with Brussels before a vote in parliament next week. Her calls on Thursday included to Len McCluskey, the head of Britain's biggest union and an ally of opposition Labour Party leader Jeremy Corbyn.

"The prime minister is seeking the widest possible support for her deal ... It is a good deal for workers," the spokeswoman said, adding that May would have further engagement with business groups and trade unions in the coming days.

(Reporting by Kylie MacLellan, writing by William James, editing by Elizabeth Piper)