The key thing to remember is that Britain is a parliamentary democracy, and there is a clear majority in Parliament against a no-deal exit. Parliament will ensure, in my view, that that does not happen. Philip Hammond chancellor of the exchequer, United Kingdom

British lawmakers thrice voted down the agreement that May negotiated with the EU, despite European leaders consistently claiming they would not reopen negotiations. Leaving the EU without a deal is seen by many as the U.K.'s default option if Parliament doesn't pass May's agreement. "Very small — that's the key message," Hammond said when CNBC's Nancy Hungerford asked about the likelihood of a no-deal Brexit happening. Hammond's role as chancellor of the exchequer is the rough equivalent of a finance minister.

"The key thing to remember is that Britain is a parliamentary democracy, and there is a clear majority in Parliament against a no-deal exit. Parliament will ensure, in my view, that that does not happen," he said at the G-20 Summit and Ministerial Meetings in Japan.

What 'no-deal' means

Exiting the EU without a negotiated deal would mean the U.K. abruptly ceasing to be a member of the bloc once the deadline to exit is over. Among other things, such a situation would result in Britain carrying out trade with the EU according to rules by the World Trade Organization — which apply higher tariffs on products an array of products including such things as automobiles and dairy products. Such a situation would continue until both sides reached an agreement to define their new relationship.

We can't have a solution where half the country feels it has won a great victory and the other half feels it's been completely defeated. Philip Hammond chancellor of the exchequer, United Kingdom

Several contenders to succeed May have publicly said that if they became prime minister, they would take the U.K. out by the current deadline on Oct. 31, with or without a deal. Such contenders include the former foreign secretary, Boris Johnson, the former Brexit secretary Dominic Raab, and Esther McVey, former work and pensions secretary. Hammond said it's "unwise" for candidates to make such a specific pledge, because they will face difficulties in persuading lawmakers to back a no-deal Brexit. "One thing is indisputable: If a prime minister defies the will of Parliament, he or she can expect some trouble from Parliament. So the political reality is that in a parliamentary democracy, on big decisions, government has to be mindful of the position of Parliament," he said.