The tests began Monday morning and are intended to gauge how severe the disruption would be if Britain leaves the European Union on March 29 without an agreed upon withdrawal deal.

It is expected that an abrupt departure without a deal would lead to the introduction of tariff and customs barriers that would slow fast-moving ferry and rail traffic that links Britain to continental Europe. There are concerns that major traffic jams leading into and out of ferry ports like Dover could greatly hamper trade and leave Britain without adequate food and medicine.

Parliament is expected to resume its debate over the government's planned withdrawal deal Wednesday, with a vote tentatively scheduled for early next week.

There are no indications that lobbying over the holidays has garnered Prime Minister Theresa May more support for her plan, which has sparked wide opposition in Parliament. A vote that had been scheduled in November was delayed as May admitted it would face certain defeat.

The prospect of the bill's possible defeat next week has renewed concern about the "no-deal" situation that Britain would face as the withdrawal date approaches without any arrangements in place.

Fears about economic disruption Monday sparked roughly 200 legislators including some from the prime minister's Conservative Party to write to May asking her to rule out the no-deal scenario.

May has not spelled out how she will respond if the withdrawal bill is voted down next week.

Brexit minister Kwasi Kwarteng said Monday that the government is still focused on winning the vote.

"A week is a very long time in politics. We don't know what the numbers are," he told BBC. "We have got a week. I think the situation — as it always does — has developed, it evolves. I am very hopeful that the deal will be voted through next week."