A coronavirus mutation first identified in Bristol has been designated a “variant of concern” by UK government scientists.

It is the fourth “variant of concern” identified by the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag).

The other three were first found in Kent in southern England, South Africa, and Brazil.

Meanwhile, door-to-door “surge” testing is to take place in parts of Lambeth in south London after the South Africa variant was found in the area.

The Bristol mutation is a variant of the B117 strain identified in Kent whose rapid spread and transmissibility led to the cancellation of Britain’s planned Christmas lockdown relaxation with just days’ notice. It also carries the E484K mutation, which experts suggest may be better at evading the human immune response.

A variant first seen in Liverpool has also now been named as a variant “under investigation”, the second of these. Variants of concern are first designated “variant under investigation” before in some cases receiving the more serious title after consideration by Nervtag.

The scientists say they have a “high degree of confidence” that the vaccines will work against the new variants.

So far Public Health England has identified 21 cases of the Bristol variant.

In Lambeth, the surge testing and genomic sequencing will be carried out in the SE27 0, SE27 9 and SW16 2 postcodes.

People living within the targeted areas are strongly encouraged to take a Covid-19 test this week, whether they are showing symptoms or not.

People with symptoms should book a test in the usual way while others should visit their council website.

Meanwhile the surge testing carried out in Woking is now complete, the Department of Health and Social Care said.

New variants emerge regularly and experts are conducting frequent analysis to see which are of concern, and which are not.

The Kent variant was first detected in the UK and was first sequenced in September, and it has been suggested that its spread in December led to a rapid rise in Covid-19 cases before the second national lockdown was announced in England.

It is now thought to be the dominant variant in the UK.

Analysis of the variant, known as B117, suggests it is up to 70% more transmissible than the previous strain that was dominant in the UK.

Around 170 cases of the South African variant have been detected in the UK.

No cases of the Brazilian variant of concern have been detected in the UK.

Like the South African variant, the Brazilian one carries a mutation in the spike protein called E484K, raising concerns that vaccines may not be as effective against it.

The other variant from Brazil has been detected in the UK, but experts say it is no cause for concern.