Prime Minister Theresa May faces a crunch week for her leadership and Brexit plan, with ministers and backbenchers in her Conservative Party feuding over Britain's future ties to the European Union.

May issued a plea for unity in an opinion piece in the Sunday Times newspaper, calling on Brexiters to "trust me to deliver." "I will not let you down," she wrote.

Less than a year until the U.K. leaves the EU, the government still hasn't reached a consensus on what to seek in exit negotiations. Pro-Brexit ministers in May's inner "war Cabinet" — which meets Tuesday — oppose her idea to maintain close customs relations with the bloc, a plan Foreign Secretary Boris Johnson labeled "crazy." The Sunday Telegraph also reported that at least 12 members in the full Cabinet of 28 are set to oppose it.