Labour leader Keir Starmer has called for a "four nations together" approach for easing coronavirus lock-down restrictions.
Mr Starmer, who became party leader last month, said there had been an "incredible sense of solidarity" across the UK but the relationship between Wales, England, Scotland and Northern Ireland "could" be put under strain if there was an increasing divergence in approaches from the respective governments to coronavirus.
Mr Starmer was speaking on the BBC's Politics Wales programme one week after British Prime Minister Boris Johnston told people in England that they could "drive to other destinations" for exercise and leisure, during a live broadcast
In Wales, the Welsh Government re-stated people cannot travel "a significant distance" from home for exercise.
The Labour leader blamed Mr Johnson for the way Wales and England had diverged in the easing of the lockdown.
"I do think responsibility for that lies very largely with the prime minister, who I would have hoped could have got all the ducks in a row before he actually made his speech last Sunday," he said.
"The sooner, frankly, we get back to operating as four nations together the better," he said.
Mr Starmer said he was "constantly asked to compare and contrast" the British and Welsh governments' response to the pandemic however had "refused to get into that because I don't think people want to hear that".
"What I've said is that the Labour party, certainly in the UK Government, will be a constructive opposition and what I meant by that is having the courage to say we'll support the government when that's the right thing to do," he said.
