Penny Mordaunt, Mrs Leadsom’s campaign manager, said: “This is a great result. Andrea was the least known candidate but she is now clearly the one with momentum going forward.
“She is a fresh face in this contest but she has won colleagues over with a clear vision on leaving Europe and has been recognised as a real expert on the subject.
“She also has a passion for social reform which is what the result of the referendum showed us we really need.
“A May/Leadsom final two put before members is going to be very exciting.”
Former Cabinet minister John Redwood, a Leadsom backer, said: “This is a fantastic result.
“It now looks like it will be a contest between her and Mrs May and once she gets out into the country, has some media coverage, members will begin to know who she is and what she is about and I am sure she can win.”
While Stewart Jackson, who is backing energy minister Ms Leadsom, said her supporters were “very pleased” with tonight’s result.
He added: “It’s a solid return. I think this shows she is ready to go all the way.”
The Peterborough MP said the support for Ms Leadsom showed Mrs May would not be allowed a “coronation” as the new Tory leader and prime minister.