Experts have raised concern over the growing number of cases of a new Covid-19 variant that first emerged in India.

Public Health England (PHE) reported that 73 cases of the B.1.617 variant have been found in England, as well as four cases in Scotland.

The figure of 77 cases comes from the latest update of PHE’s surveillance of the distribution of different variants across the UK, based on data up to April 7

Officials have currently designated it a “variant under investigation” (VUI) rather than a “variant of concern” (VOC), such as the Brazilian Manaus or South African variants.

Meanwhile, 600 people in the UK have now contracted the South African coronavirus variant, with an extra 56 cases being reported this week.

PHE has not disclosed whether the figure includes cases detected as a result of surge testing. In London, extra testing facilities were launched this week to help limit the spread of the variant following a cluster of cases being discovered.

Of the coronavirus variant first discovered in India, Danny Altmann, professor of immunology at Imperial College, said it was likely to be escalated to a VOC.

Officials said there is currently no evidence to suggest that disease from the newly identified variant is more serious than previous ones, nor is there current evidence to suggest vaccines are less likely to work against it.

It is understood that the cases detected in England are dispersed across different parts of the country and many are linked to international travel, but investigations are under way.

According to PHE, the variant “includes a number of mutations including E484Q, L452R, and P681R”.

PHE said that mutations of the 484 spike protein have been associated with the Manaus and South African variants.

The E484K mutation is reported to result in weaker neutralisation by antibodies in lab experiments, but the E484Q mutation is different and still subject to investigation.

Viruses by their nature mutate often, with more than 18,000 mutations discovered over the course of the Covid-19 pandemic, the overwhelming majority of which have no effect on the behaviour of the virus.

PHE’s latest findings mean there are now seven VUIs and four VOCs being tracked by scientists in the UK.

Professor Altmann told BBC Radio 4’s PM: “I think we should be terribly concerned about it.

“It is similar to the ones we know about – it mixes and matches some of the features we’ve seen before with this E484 change that we’ve seen before in a similar but different version in South Africa and Brazil, and then the infectivity change that we saw in the Californian variant.

“As we keep saying, it is the infectivity change plus the new evasion.

“This isn’t a ‘variant of concern’ yet but I suspect it will be.

“I look at all of them and they are things that can most scupper our escape plan at the moment and give us a third wave. They are a worry.”

In India, Covid-19 rates are soaring, with more than 13.9 million confirmed cases and 172,000 deaths.

The country is not currently on the government’s “red list” for travel, which sees people who have been in those countries in the previous 10 days refused entry to the UK.

British or Irish nationals, or people with UK residency rights, are able to return from red list countries but must isolate in a quarantine hotel for 10 days.

Professor Altmann said he thought India “ought” to be placed on the red list of countries from which travellers are required to embark on a hotel quarantine upon arrival in England.

The Imperial College expert said: “I find this a bit mystifying.

“Obviously policy is not my area of expertise, but as a scientist I find it slightly confounding.

“I know their variant hasn’t been proved to be responsible for their 200,000 cases per day but it is implicated in quite a high proportion of the genetic sequencing.

“So it looks to me like it probably ought to be a red-listed country, as far as I can see.”

Boris Johnson’s visit to India will still go ahead despite the soaring coronavirus cases in the country.

The prime minister had already scaled down his at the end of April due to the country’s worsening coronavirus situation, but Downing Street has insisted it will still go ahead.

A No 10 spokesman told a Westminster briefing: “The prime minister’s visit is still happening later this month.

“We have said that the programme will be slightly shorter than it will have been, and you can expect the main body of his programme to take place on Monday April 26.

“As you would expect, safety is obviously important and is a priority for us on this trip, which is why we will make sure that all elements of the visit are Covid-secure.”

Johnson was due to spend four days in the south Asian country at the end of the month but, following talks with Narendra Modi’s administration, the “bulk” of the meetings could be fitted into one day.

Asked why India has not been put on the red list despite the soaring number of cases, Downing Street said the situation is “under constant review”.

A No 10 spokesman told reporters: “We add and remove countries based on the latest scientific data and public health advice from a range of world-leading experts.

“We keep it under constant review and we won’t hesitate to introduce tougher restrictions and add countries if we think it is necessary.”

But Labour said the blame for the Indian mutation making its way into Britain “rests squarely with the UK government”.

Shadow home secretary Nick Thomas-Symonds said: “Ministers have been warned time and again that failing to introduce a comprehensive hotel quarantine policy would leave us exposed to variants of Covid.”