Ireland’s deputy prime minister has urged caution in Westminster over speculation that a Brexit deal could be struck in the next few days.

Simon Coveney, the tánaiste, spoke amid concern in Brussels and Dublin that the Conservative party was again “negotiating with themselves” over Brexit and mistakenly considering a cabinet decision as “end of story”.

Sources say the British government has yet to share any wording of the contentious backstop proposal to keep the Irish border open in the event of no deal and that this alone will take days to scrutinise before agreement can be reached.

“Can I just say this in relation to commentary today, particularly in British media: I would urge caution; an imminent breakthrough is not necessarily to be taken for granted, not by a long shot,” the tánaiste said in Dublin on Thursday, after a speech to the Canada Business Association.

“Repeatedly people seem to make the same mistake over and over again, assuming that if the British cabinet agrees something, then that is it, everything is agreed. This is a negotiation and needs to be an agreement of course between the British government, but also between the 27 countries and Michel Barnier and his negotiating team.

“I would urge caution that people don’t get carried away on the back of rumour.”

The European agriculture commissioner, Phil Hogan, told the Irish broadcaster RTÉ that unless Britain produced its proposals for the Irish border within the “next few days” a November deal was unlikely.

“I would say, if I was a betting person, we would have a December council to discuss the final outcome and hopefully we can do a deal,” he said.

He insisted Britain could not backslide on the backstop it agreed to in December last year and that the EU was waiting for proposals from the UK about how it could adapt its position to accommodate the agreement it has already made in relation to the backstop.

Speculation that Theresa May could secure a deal within the next week grew in the last 48 hours with the possibility of a special meeting this weekend to get cabinet approval.

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Cabinet members were invited into a reading room to see the draft withdrawal agreement on Wednesday but, critically, the documents did not include any text on the Irish border backstop arrangement.

Downing Street has insisted the documents show “where we are so far” and that the development “does not imply that a deal has been done”.

The EU has already said that it would need a strong signal from Britain this week that it was close to an agreed position if a special EU council summit were to be held to sign off the final deal.

The backstop will involve a complicated arrangement that must satisfy EU requirements that it does not have an expiry date or an option of a unilateral exit for the UK.

In the past 24 hours Ireland’s prime minister, Leo Varadkar, has also said he thinks anticipation of a November deal is misplaced.

“The possibility of getting a special summit in November becomes less likely, but we do have one scheduled anyway for 13 December,” he told reporters in Helsinki.

“Not getting it done in November doesn’t mean we can’t get it done in the first two weeks of December; beyond that we’d be into the new year but that wouldn’t be a good thing.”