Brexit referendum

British Conservative party leadership and prime minister contender Boris Johnson leaves his home in south London, Thursday June 20, 2019. The race to become Britain's next prime minister is down to the final four on Wednesday, as Boris Johnson stretched his lead among Conservative lawmakers and upstart Rory Stewart was eliminated from the contest. (AP Photo/Matt Dunham)

Britain's Conservative Party leadership contender Boris Johnson leaves his home in south London, Wednesday June 19, 2019. Former Foreign Secretary Boris Johnson increased his lead in the race to become Britain's next prime minister Tuesday in a Conservative Party vote that eliminated one of his rivals and enabled upstart candidate Rory Stewart to defy expectations by remaining in the contest. (Dominic Lipinski/PA via AP)

British Conservative Party leadership contender Boris Johnson arrives for a live TV debate in central London Tuesday, June 18, 2019. Britain's Conservative Party will continue to hold elimination votes until the final two contenders will be put to a vote of party members nationwide, with the winner due to replace Prime Minister Theresa May as party leader and prime minister.(AP Photo/Vudi Xhymshiti)

British Conservative party leadership contender Boris Johnson gets in a car as he leaves his home in south London, Tuesday, June 18, 2019. Contenders for leadership in Britain's ruling Conservative Party to become the next Prime Minister, jostled for attention Monday as the race narrowed into a contest to seize the mantle of challenger to front-runner Boris Johnson. (AP Photo/Matt Dunham)

Conservative party leadership contender Boris Johnson leaves his home in London, Monday June 17, 2019. Candidates seeking to beat Boris Johnson and become Britain's next prime minister accused the Brexit-backing front runner of trying to avoid scrutiny after he refused to take part in a televised debate alongside his five rivals Sunday. (Jonathan Brady/PA via AP)

FILE - In this file photo dated Friday, June 7, 2019, a police officer stands guard outside the front door to the official residence of Britain's Prime Minister, 10 Downing Street, London. Lawmakers are set to narrow the field of contenders for leadership of the Conservative Party and Prime Minister, in a series of elimination votes over the coming days from Monday June 17, 2019, with the final two names put to a vote of Conservative party members nationwide. The six contenders to replace Prime Minister Theresa May are: Michael Gove, Jeremy Hunt, Sajid Javid, Boris Johnson, Dominic Raab, Rory Stewart. (AP Photo/Matt Dunham, FILE)

British Conservative party lawmaker Boris Johnson leaves home in south London, Friday, June 14, 2019. Johnson is a leading candidate in the Conservative Party leadership campaign to be the next British Prime Minister. (AP Photo/Alastair Grant)

FILE - In this file photo dated Monday, April 1, 2019, Britain's lawmaker Chuka Umunna arrives at 10 Downing Street for a knife crime summit in London. Umunna quit the Labour Party earlier this year to help form a pro-European new political party, but has now moved to join the centrist Liberal Democrats, and is quoted Friday June 14, 2019, in The Times of London, saying the Lib Dems are best placed to stop Brexit.(AP Photo/Frank Augstein, FILE)

Britain's Conservative Party lawmaker Boris Johnson gestures as he speaks during the official launch of his leadership campaign, in London, Wednesday June 12, 2019. Boris Johnson solidified his front-runner status in the race to become Britain's next prime minister on Tuesday, gaining backing from leading pro-Brexit lawmakers.(AP Photo/Frank Augstein)

Scotland's First Minister Nicola Sturgeon speaks during an event in Brussels Tuesday, June 11, 2019. Scottish First Minister Nicola Sturgeon is in Brussels Tuesday to meet with European Union chief Brexit negotiator Michel Barnier and European Commission President Jean-Claude Juncker. (AP Photo/Virginia Mayo)