Senior ministers were invited to review the text of the withdrawal agreement that has so far been secured in negotiations with Brussels, and are poised to meet as soon as a deal is ready to be signed off.
"I would urge caution that an imminent breakthrough is not necessarily to be taken for granted, not by a long shot", Coveney said on Thursday.
"It is important that Britain would not undercut our own products on our own market in the all-UK Irish backstop", one source said of the European Union demand that comes as the two sides are seeking a Brexit deal as soon as this month.
He went on: "Repeatedly, people seem to make the same mistake over and over again-assuming that if the British cabinet agrees something then that's it then: everything is agreed".
Former Brexit secretary David Davis said the full government legal advice on Brexit must be published and insisted how the United Kingdom could exit from the customs union must be "pinned down" before MPs and peers vote on the deal.
The European plan, known as the "backstop to the backstop", would leave Northern Ireland tied to the single market and customs union if Brexit talks collapse.
Although 95 per cent of a Brexit deal is said to be agreed, Britain and the European Union have yet to agree on how to guarantee that there will be no return to a visible border between Northern Ireland and the Republic of Ireland in the future.
Some cabinet ministers want to see the full legal advice given to May setting out how any customs arrangement could be ended to avoid it becoming a permanent settlement. Progress on the Irish backstop could seal the withdrawal agreement, but a deal would not have been completed until all details of the future framework were also tied up.
May will still need to get the deal, including the so-called Irish border backstop plan, approved by her Cabinet and later by Parliament - where she's likely to face considerable opposition.
May's spokesman said ministers agreed at cabinet on the need for an "effective mechanism" within the backstop to ensure "that the United Kingdom can not be held in the arrangement indefinitely".
A UK-wide customs deal would maintain quota-free and tariff-free access to European markets for the British fishing industry and in return the EU wants to keep continued access to United Kingdom waters for its trawlers, the newspaper said.
Michel Barnier cited the anti-EU British MEP Nigel Farage as a cautionary example at a conference of the centre-right European People's Party.