Number 10 has blamed the Welsh and Scottish Governments for the postponement of a four-nation summit to discuss Covid recovery plans.
A spokesman described it as “disappointing” and said no new date had yet been scheduled.
But the Welsh Government said the meeting should be “done properly, not some rushed tick box or PR exercise.”
The virtual meeting, along with the leader and deputy leader of Northern Ireland, was due to be held tomorrow (Thursday.)
It had been promised by the Prime Minister in his letter of congratulations to Mark Drakeford and Nicola Sturgeon following their election successes.
Yesterday, the Welsh and Scottish leaders wrote a joint letter to the Prime Minister criticising the lack of a detailed agenda and asked for it to be postponed for more preparation.
Confirming that the meeting was called off, the Prime Minister’s official spokesman said: “We had scheduled for this meeting to happen tomorrow.
"As the Prime Minister set out, we need to overcome the significant challenges of the Covid recovery with the same spirit of unity and cooperation shown during the pandemic, so it is disappointing that the Scottish and Welsh governments would prefer to delay this meeting so that they have more time to prepare, especially given the scale of the challenge.
"But we remain committed to that spirit of cooperation.”
Asked if a new date had been set, the spokesman said: “The Prime Minister is keen to speak to the First Ministers and the First and Deputy First Ministers of Northern Ireland about recovery. We want to do that as soon as possible but we don't have a date set.”
It was, he said, effectively up to the First Ministers to suggest a new date, adding: “We want to work with them to find a new date to schedule this, now that they aren't able to do tomorrow.”
The Welsh Government didn’t want to add to comments made in the First Ministers’ letter, but a source reiterated those remarks: “We really want it to be done properly. Not some rushed tick box or PR exercise that fails to achieve anything of substance.”
The leader of the Welsh Liberal Democrats, Jane Dodds, called for the meeting to be rearranged quickly, adding: “For Boris to cancel this meeting at the last minute with no reason shows how little Boris cares about the nations of the United Kingdom."