Brexit secretary David Davis has resigned from his Cabinet position on Sunday night, after saying he did not “believe” in Theresa May’s strategy.

After nearly two years in his role, Davis tendered his resignation on Sunday saying that “the current trend of policy and tactics” was making it “look less and less likely” that the UK would leave the customs union and single market.

In his letter, he added that he was “unpersuaded” that the government’s negotiating approach “will not just lead to further demands for concessions” from Brussels.

He concluded by saying that “that the national interest requires a Secretary of State in my Department that is an enthusiastic believer in your approach, and not merely a reluctant conscript.”

The resignation will come as a blow to Prime Minister Theresa May, possibly underscoring the lack of progress that has been made in negotiations since the vote in 2016.

One or two of Davis’ junior ministers are expected to resign as well.

Theresa May responded by thanking Davis for his service, but adding: “I do not agree with your characterisation of the policy we agreed at Cabinet on Friday.”

Cabinet agreed a policy for progressing forward with the negotiations, which Davis said may “just lead to further demands for concession”.