Brexit Secretary David Davis will attempt to reassure EU negotiators over Britain's plan to guarantee the future rights of European nationals living in the UK amid deep scepticism in Brussels.
Mr Davis returns to the negotiating table in the Belgian capital for the second round of talks with the European Commission's chief negotiator Michel Barnier.
The meeting takes place against a backdrop of increasingly bitter and public feuding among UK ministers over the Government's Brexit strategy.
Over the weekend, Chancellor Philip Hammond angrily accused Cabinet rivals of trying to undermine his agenda for a "softer" business-friendly Brexit prioritising jobs and the economy.
One unnamed Cabinet minister was reported have hit back, claiming Mr Hammond was part of an attempt by "the Establishment" to prevent Britain ever leaving the EU.
The Daily Telegraph quoted the minister as saying: "What's really going on is that the Establishment, the Treasury, is trying to f*** it up. They want to frustrate Brexit."
The rowing will be seen as further evidence of Theresa May's weakness after seeing her Commons majority wiped out in last month's general election.
After what Mr Davis said was a "good start" in the opening session of the Brexit negotiations last month, the mood between London and Brussels has soured following a series of public spats.
It began with the publication of what Britain said was a "fair and serious" offer to guarantee the future rights of the 3.2 million EU citizens living in the UK and the 1.2 million British ex-pats in the EU.
The proposal to grant EU nationals "settled status", effectively indefinite leave to remain, was immediately dismissed by European Council President Donald Tusk as "below our expectations", and risked worsening their situation.
Foreign Secretary Boris Johnson then fanned the flames when he said in the Commons that Brussels could "go whistle" if it expected the UK to pay a hefty "divorce bill" in respect of its outstanding financial obligations.
Mr Barnier, who has made clear that he is not prepared to start talks on a trade deal until there has been sufficient progress on the financial settlement, retorted icily he could not hear any whistling, "just the clock ticking".
That row was quietly defused with a written Government statement acknowledging Britain had obligations to the EU which would continue after the UK had left and which "need to be resolved"
However ministers also faced criticism at home over their plans to withdraw from the EU nuclear regulator, Euratom, amid warnings the UK find its access to radioactive isotopes used to treat cancer restricted.
All three issues will be on the agenda for this week's discussions, which are expected to continue to Thursday, along with the thorny matter of the future border between Northern Ireland and the Republic.
Mr Davis made clear his first priority would be resolving the issue of citizens' rights, saying he was determined to make "real progress".
"We made a good start last month, and this week we'll be getting into the real substance," he said.
"Protecting the rights of all our citizens is the priority for me going into this round and I'm clear that it's something we must make real progress on."
Transport Secretary Chris Grayling attempted to play down suggestions of Cabinet splits and criticised those who have been briefing about its meetings.
“I don’t see these great divisions that are suggested to me in the Sunday newspapers and I have to say I think all of this is somewhat overplayed,” he told BBC Radio 4's Today programme.
Mr Grayling said the suggestion that there were "profound and fundamental differences" between Cabinet ministers on Brexit were "a bit exaggerated", but admitted: "We're not a group of clones, we have discussions around the Cabinet table and outside Cabinet, we debate issues, we decide what's right and then we get on with it.
"I'm very clear that the Cabinet and the party are united behind Theresa May, united in determination to get the right deal for the country in the Brexit negotiations and to make sure we continue the economic progress we’ve made."