Theresa May has said she is "honoured and humbled" to have been chosen as the new leader of the Conservative Party and UK prime minister. Speaking outside Parliament, the PM-in-waiting pledged to build a "better Britain" and make Brexit a "success". David Cameron is to tender his resignation to the Queen on Wednesday. It comes after Mrs May's only rival to succeed Mr Cameron as Conservative leader, Andrea Leadsom, pulled out of the contest earlier on Monday. Mrs May paid tribute to Mrs Leadsom for her "dignity" and praised Mr Cameron's "leadership" of the party and country. Mr Cameron, PM since 2010, decided to quit after the UK's Brexit vote.