Downing Street has denied that a NHS Test and Trace delay in alerting local authorities in hotspot areas to positive cases helped contribute to the spread of the Indian variant.

It follows a report by the BBC that for three weeks in April and May, eight local authorities in England – including Blackburn with Darwen – did not have access to the full data on positive tests in their area, meaning more than 700 cases were not reported and traced locally.

Surge testing and vaccinating has been taking place in Blackburn in Lancashire, along with a number of other impacted areas in the UK, after cases of the B1617.2 mutation increased.

Data is still being established on whether the vaccines being rolled out in the UK will prevent serious illness from the highly transmissible Indian variant, with fears its spread could prevent the Prime Minister from lifting all coronavirus restrictions in England next month.

The BBC said a report into the reporting glitch at one of the councils affected concluded that the rapid spread of Indian strain within its boundary was “exacerbated by the sporadic failure of the national Test and Trace system”.

Labour said the suggestion that local public health officials had been “left in the dark” over their case numbers “beggars belief”.

But No 10 said the issue – with Blackburn reportedly having the highest number of missing cases – was “quickly resolved”.

The Prime Minister’s official spokesman told reporters: “In this specific instance, all positive cases were contacted and told to self-isolate for 10 days.

“As you know, there was a short delay when asking some of those positive cases to provide details of individuals they had contacted since contracting Covid.

“This issue was across a small number of local authority areas and was quickly resolved.”

Asked whether the Government accepted the failure contributed to the spread of the variant, the spokesman said: “The spread of the variant will be down to a number of factors – this was an issue that occurred across a small number of local authority areas, so I don’t think it is possible to draw that conclusion from this.”

Labour shadow health secretary Jonathan Ashworth said: “This is deja vu and echoes the mistakes made last year with Boris Johnson’s ‘whack-a-mole’ approach.

“It beggars belief that yet again local health experts on ground have been left in the dark for two weeks when we know acting with speed is vital to containing an outbreak.

“Ministers need to explain what’s gone wrong and provide local health directors with all the resources they need to push infections down.”

Councillor Mohammed Khan, leader of Blackburn with Darwen Council, said: “We can confirm that the details as outlined in the BBC news story are broadly accurate.

“This situation has had an effect on the residents of our borough.

“Unfortunately, the technical problem in the national Test and Trace system happened just at the time the borough had incoming cases of travel-related cases of the Covid variant first identified in India.

“However, the national Test and Trace system issues have now been resolved.”

Blackpool’s director of public health confirmed the local authority was another of the eight impacted, with York, Bath and North East Somerset, Bristol, North Somerset, Southend-on-Sea and Thurrock said to be among those affected.

Dr Arif Rajpura said Blackpool “only had a very small number of cases that were not visible” via the central system but that a low case rate in the resort meant “this technical glitch has not had an impact on the spread of the Indian variant here”.

No 10 said it was “still too early” to determine whether the Indian variant could delay scrapping all Covid measures on June 21 but that there had “not been any significant changes that currently suggest we need to change our course of action”.