The UK’s coronavirus policy risks descending into chaos after the Scottish and Welsh governments accused Boris Johnson’s administration of ignoring scientific advice, amid increasingly different stances among the devolved nations. Although the prime minister insisted the UK was “proceeding as one” in its response to Covid-19, varying versions of events have emerged over how decisions were made about travellers returning from Portugal and Greece. While ministers opted not to put Portugal back on the list of countries requiring a 14-day quarantine period for English travellers, Scotland and Wales disagreed. The Scottish government said the English decision was made before ministers had properly considered data from the government’s Joint Biosecurity Centre (JBC). Separately, the Welsh health minister, Vaughan Gething, told the Guardian that data from the JBC on infections in Portugal was “clear” in pointing towards renewed quarantine. The row risks further undermining confidence in the largely voluntary system under which travellers returning from countries seen as high risk isolate entirely for two weeks. It is also increasingly unpopular with many Conservative MPs, who are pushing for a system of testing those arriving in the UK for Covid-19 to either reduce or eliminate the need for quarantine, an alternative heavily backed by airports. The UK’s previous near-unanimity on quarantine was shattered this week with the decision of the Scottish and then Welsh governments to reimpose quarantine for travellers arriving from some or all parts of Greece and Portugal. Currently, people returning from the countries to addresses in England and Northern Ireland still face no restrictions, with Grant Shapps, the transport secretary, announcing on Thursday evening that no immediate changes would be made. But those coming back to Scotland from anywhere in Greece and Portugal have to quarantine. Wales has also imposed restrictions, but only for people travelling from half a dozen of Greek islands, and just for mainland Portugal. Adding to the complexity, quarantine-free travel from Gibraltar exists to England and Scotland, but not to the other devolved nations, while French Polynesia is on the safe list only for England and Northern Ireland. Speaking on Friday, Shapps accused Scotland of having “jumped the gun” in deciding to impose quarantine on Greece, saying this risked creating confusion. A Scottish government spokesperson said the decision was taken because of a “worrying number” of positive Covid tests among people who had recently returned from Greece, and in turn said the UK government made its decision on Portugal before considering the latest data. They said: “In the case of Portugal, it was unfortunate that the UK government announced their decision yesterday before ministers from England, Scotland and Northern Ireland met and before considering the latest Joint Biosecurity Centre data. This indicated a significant rise in both the prevalence of the virus in Portugal and in test positivity.” The Scottish government has expressed frustration in recent weeks at suggestions from UK government sources that they have come under unreasonable pressure over quarantine lists. Gething said he had hoped to have meetings between the four nations before the Welsh government made its decision on Greece and Portugal, but UK ministers had not been available. He said: “The JBC report was really clear on Greece, it said overall it’s a moderate risk. However they note a high risk to UK public health from travellers returning from geographically dispersed Greek island groups. “I don’t see how you can have direct advice of high risk to public health and not take action. I have to do what I think is right.” On Portugal, he said: “The advice was clear. They [the JBC] had upped the risk rating because of an increase in positive cases per 100,000, well above our normal threshold for taking action.” Asked if he was frustrated at the different approaches from the devolved nations, he said: “We should have had a meeting on Wednesday or Thursday morning.” The meeting finally took place at 6pm on Thursday, by which time the Welsh government had already decided to bring in extra quarantine measures. Speaking on a visit to Solihull, Johnson dismissed the idea that unanimity on the policy was collapsing. “The reality is that different devolved administrations in the UK, Scotland, Wales and Northern Ireland, they have different rates of infectivity, different approaches to the problem,” he said. “But overwhelmingly the UK is proceeding as one. I think you will find if you dig below the surface, of some of the surface differentiations, you will find overwhelmingly the UK takes the same approach.”