Ministers have destroyed the public’s trust in travel quarantine rules, a former government adviser has said, as Labour MPs claimed the changes for England were politically motivated rather than based on public health.

The criticism came after the latest update to the traffic light system that grades countries depending on their Covid case, vaccine and variant rate, in which a host of European destinations moved to the green list while others were downgraded from red to amber.

The transport secretary hailed the announcement as good news for travellers and the travel industry, but said restrictions on passengers would probably last into the autumn, and predicted countries may require people to be fully vaccinated “for evermore” to avoid isolation on arrival.

Grant Shapps said people would “have to settle down into knowing that this will happen” but that as more countries’ populations become inoculated “things will start to become more routine”.

Pressure is growing on the government to publish the rationale behind ministers’ decisions, including the methodology and breakdown of specific figures for each country.

The latest developments come as the UK’s daily coronavirus case rate surpassed 30,000 for the first time in more than a week. There were 30,215 new cases reported on Thursday, along with 86 deaths within 28 days of a positive test.

The Joint Biosecurity Centre (JBC) provide the government advice, but it is up to politicians to decide which changes should be made every three weeks to the red, amber and green lists. The Office for Statistics Regulation recently rebuked Whitehall for “not making the data and sources clear”.

The Labour MP Yasmin Qureshi said the system was “becoming a politically motivated policy, which seeks to pander to foreign governments whom the UK government feel they have a potential for economic benefit or profit”.

She hit out at the decision to upgrade places such as India to the amber list while leaving Pakistan on the red list, saying Pakistan was “clearly not in the UK’s designs for ‘global Britain’” and had a lower positivity rate than India, where the Delta variant was discovered.

“Many of these decisions appear arbitrary and without reason,” she said.

Ben Bradshaw, a Labour MP and member of the Commons transport committee, said decisions about the traffic light system were an “absolute scandal” and had “nothing to do with public health and everything to do with politics”. He cited Johnson’s initial two-week delay in putting India on the red list in April.

“The government has repeatedly failed to publish the detailed data on which its decisions are made,” he said. “Every other country in Europe does this, so the public and business can plan. Air passenger numbers in Europe have already recovered to about 60% of pre-Covid levels, while the UK figure is 16%.

“When the public inquiry into Covid happens, the government’s policy on travel is going to be a major focus. It has resulted in the worst of all worlds – one of the highest Covid death rates and the completely unnecessary trashing of thousands of jobs and businesses in our vital transport sector and the prolonged enforced separation of millions of families and loved ones.”

The Welsh government announced on Thursday that it would mirror the relaxation, meaning it now applies to the whole of the UK.

Peter Ricketts, a former senior Foreign Office adviser and ambassador in Parispicked up on the chaos caused by France’s earlier placement on the “amber plus” list, making it the only amber-list country from where travellers still had to quarantine for up to 10 days even if fully vaccinated.

He said ministers’ use of the traffic light system was perceived by the public as “arbitrary and poorly explained, and the constant tinkering has confused people and lost their trust”.

Pointing to the confusion about the treatment of France, which is expected to go back on the regular amber list from 4am this Sunday, Lord Ricketts said it was not surprising a French minister had accused the UK of discrimination. The move had severely affected bilateral relations and it would “take time to repair the damage”, he said.

Rosa Hodgkin, a researcher at the Institute for Government, said it was “very difficult to effectively scrutinise” decisions because of the JBC’s refusal to reveal how it weighs different data and ministers’ also taking into account other factors.

“Having such an opaque system leaves ministers open to the charge that decisions are politically motivated because it is very difficult to say definitively what decisions are based on,” she said.

The Department for Transport was contacted for comment.