British Prime Minister Theresa May leaves 10 Downing Street in central London, on January 18, 2017, before attending the weekly Prime Minister's Questions (PMQs) at the House of Commons. British business leaders welcomed May on her Brexit clarity, following her speech yesterday, but insisted the UK prime minister must deliver on her pledge to secure access to the EU single market. / AFP / Isabel INFANTES (Photo credit should read ISABEL INFANTES/AFP/Getty Images)

British Prime Minister Theresa May leaves 10 Downing Street in central London, on January 18, 2017, before attending the weekly Prime Minister's Questions (PMQs) at the House of Commons.
British business leaders welcomed May on her Brexit clarity, following her speech yesterday, but insisted the UK prime minister must deliver on her pledge to secure access to the EU single market. / AFP / Isabel INFANTES        (Photo credit should read ISABEL INFANTES/AFP/Getty Images)

British Prime Minister Theresa May leaves 10 Downing Street in central London, on January 18, 2017, before attending the weekly Prime Minister's Questions (PMQs) at the House of Commons. British business leaders welcomed May on her Brexit clarity, following her speech yesterday, but insisted the UK prime minister must deliver on her pledge to secure access to the EU single market. / AFP / Isabel INFANTES (Photo credit should read ISABEL INFANTES/AFP/Getty Images)

British Prime Minister Theresa May leaves 10 Downing Street in central London, on January 18, 2017, before attending the weekly Prime Minister's Questions (PMQs) at the House of Commons.
British business leaders welcomed May on her Brexit clarity, following her speech yesterday, but insisted the UK prime minister must deliver on her pledge to secure access to the EU single market. / AFP / Isabel INFANTES        (Photo credit should read ISABEL INFANTES/AFP/Getty Images)

British Prime Minister Theresa May leaves 10 Downing Street in central London on January 11, 2017 to attend the weekly Prime Ministers Questions session in the House of Commons. / AFP / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images)

British Prime Minister Theresa May leaves 10 Downing Street in central London on January 11, 2017 to attend the weekly Prime Ministers Questions session in the House of Commons. / AFP / Daniel LEAL-OLIVAS        (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images)

LONDON, UNITED KINGDOM - JANUARY 25: British Prime Minister Theresa May heads to the weekly Prime Minister's Questions (PMQ) session in the House of Commons after leaving number 10 Downing Street in London, England, United Kingdom on January 25, 2017. The British government is facing increasing pressure to publish it's Brexit plans in a formal White Paper. (Photo by Kate Green/Anadolu Agency/Getty Images)

LONDON, UNITED KINGDOM - JANUARY 25: British Prime Minister Theresa May heads to the weekly Prime Minister's Questions (PMQ) session in the House of Commons after leaving number 10 Downing Street in London, England, United Kingdom on January 25, 2017. The British government is facing increasing pressure to publish it's Brexit plans in a formal White Paper. (Photo by Kate Green/Anadolu Agency/Getty Images)