According to "secret" documents obtained by the Sunday Times, the U.K. government warns of "significant" disruptions to the supply of drugs and medicine, a decrease in the availability of fresh food in the event of a no-deal Brexit.

In his first trip abroad as leader, Johnson is due to meet his European counterparts ahead of a G7 summit in Biarritz, France.

May is fighting to save her unpopular Brexit plan and her job ahead of a showdown in Parliament on Tuesday, when lawmakers are widely expected to vote down the Brexit divorce deal she struck with the European Union.