The number of cases of the Indian variant has doubled in a week, and data now shows that eight of the 10 areas with the highest rates of the strain are in the north west of England.

Bolton recorded the largest number of cases with 361 per 100,000 people for the week ending 21 May, according to an analysis of the latest data from Public Health England.

Other areas in the region with high infection rates for the B.1.617.2 variant include Blackburn with Darwen, Rossendale, Hyndburn and Burnley.

Bedford in the East of England and Leicester in the East Midlands were also among the areas with the highest case rates.

More than 200 local authority areas in England have now reported at least one infection in the most recent week for which data is available.

Health Secretary Matt Hancock said the variant is spreading and the latest estimates show it makes up more than half – and possibly as many as three-quarters – of all new COVID cases.

The variant first detected in India, which is believed to be more transmissible than the Kent variant that became dominant in the country after Christmas, has resulted in surge testing and vaccinations in numerous areas.

But even as the number of cases of the Indian variant in England more than doubled since last week – rising by 3,535 to 6,959, its impact on hospital admissions is yet to be seen.

The variant is also expected to eventually become the dominant form of COVID-19, according to chief medical officer Professor Chris Whitty.

Kirklees in West Yorkshire, although having a high number of COVID-19 cases, recorded only two cases of the Indian variant for the week ending 21 May.

Scientists believe B.1.617.2 does not cause more severe disease than the Kent variant, and indications are that vaccines are also effective.

But the government advisory body SAGE believes there is a “realistic possibility” transmissibility could be 50% higher.

Experts say that could cause a big spike in cases and hospitalisations if no restrictions are imposed.

Last week, Mr Hancock did not rule out imposing local lockdown restrictions in places worst affected by the Indian variant.

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