British Home Secretary Theresa May will become Britain's next prime minister on Wednesday after rival Andrea Leadsom dropped out of the race, saying she had not gained enough support and the country needed a new leader as soon as possible.

Outgoing Prime Minister David Cameron said May had his full support and added, "I am confident she can supply the strong leadership the country needs."

He said he expected her to be confirmed as prime minister by Wednesday. Britain's Queen Elizabeth will be consulted, although this is only a formality, and arrangements have to be made for the handover between Cameron and May.