LONDON - Shockwaves hit Britain as Brexit Secretary David Davis resigned on Monday, marked by criticism of the chaos in the ongoing Brexit process and Prime Minister Theresa May's leadership.

Davis said he hoped his decision to quit would put pressure on May so that she would not give more concessions to the European Union (EU) on a contentious trade deal.

The veteran politician, who was handpicked by May to lead Britain's journey away from the EU after the 2016 referendum, sent his letter of resignation to the PM Sunday night, just 48 hours after the cabinet agreed on a potential future trade deal with Brussels.

As May and her top advisors worked Monday morning to react to Davis's decision and appoint his successor, details emerged about why the former Brexit secretary decided to go.

In his letter to May, Davis said he is unpersuaded that Britain's negotiating approach will not lead to further demands for concessions by Brussels when the two sides negotiate on the details of their working relationship after Britain leaves.

The current trend of government policy and tactics is making it look less likely that the mandate of the referendum and the Conservative manifesto commitment to leave the EU Customs Union and single market could be delivered, he said.

"In my view the inevitable consequence of the proposed policies will be to make the supposed control by Parliament illusory rather than real," Davis added.

May said she did not agree with Davis's characterization of the policy agreed on by the cabinet when it met at her country retreat Friday.

The big questions circulating in Westminster Monday morning were whether Foreign Secretary Boris Johnson, advocate of a stronger Brexit, would also quit, and whether calls for a leadership challenge to May would gather pace.

May will face her backbench MPs in parliament where she will get the reaction to her controversial soft-Brexit plan.

An avalanche of reactions to Davis's shock decision started Monday.

Scotland's First Minister Nicola Sturgeon said, "The Chequers unity didn't last long," referring to May's cabinet meeting at her country retreat Chequers.

"This UK Government is in utter chaos and ebbing authority by the day. What a shambles," Sturgeon said.

In Cardiff, the leader of the Welsh Assembly, main opposition party Labour's Carwyn Jones, said, "The resignation of David Davis shows that the UK Government is in complete disarray over Brexit and action urgently needs to be taken to resolve this chaos -- businesses need certainty and the country needs leadership and direction."

In a radio interview in London Monday, MP Jacob Rees-Mogg, who is regarded as a potential candidate if there is a challenge to May's leadership, said the prime minister needs to give up on the Chequers proposals which, as Davis had pointed out in his resignation letter, "don't actually deliver Brexit."

However, Rees-Mogg also said he does not think a no-confidence vote against May is in the offing.

Keir Starmer, Brexit spokesperson for Labour, said in an interview Monday that Davis's resignation was a huge blow to the prime minister and made a no-deal Brexit more likely.

He said, "The Brexit secretary has resigned, effectively voting no-confidence in the prime minister and that plunges her into further chaos."

"It exposes what has been the heart of the problem all along, which is a huge division in the cabinet between those that want to stay economically close to the EU and those that want to rip up the economic model we've been operating for decades," Starmer added.