It is “possible” that putting India on the red list earlier might have prevented the widely anticipated delay to easing England’s coronavirus lockdown that is set to be announced later, a minister has said.

Boris Johnson is preparing to announce a delay of four weeks to step four of the country’s roadmap out of COVID-19 restrictions because of the spread of the Delta variant first identified in India.

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The variant now makes up more than 90% of cases in England and is estimated by Public Health England (PHE) to be 64% more transmissible than the Alpha (Kent) variant indoors.

The government has been criticised for putting India on the travel red list on 23 April – two weeks after neighbouring Pakistan and Bangladesh.

Asked if quicker action could have prevented the current situation, health minister Edward Argar told Sky News that such a suggestion was a “hypothetical” and “we don’t know is the short answer”.

“I don’t think that would have necessarily stopped the variant coming,” he insisted.

But pressed again, Mr Argar acknowledged: “It’s a hypothetical. It’s possible, but there’s no way of knowing that.”

The minister defended the government’s approach, saying ministers took “swift and decisive action”.

“We have some of the toughest border regimes in the world when it comes to tackling coronavirus and I think we acted swiftly and decisively when that was put on the list of variants of concern,” he said.