The strain, officially named AY.4.2, spreads more easily than other variants and now accounts for more than half of analysed cases in one part of the country: the Torridge area of Devon.
Officials designated the Delta Plus strain a ‘variant under investigation’ on October 20.
Scientists are still working out whether it is more transmissible or whether there are other factors helping it to spread.
Vaccines are proving as effective against Delta Plus as they are against other Delta variants, two separate studies have found.
And there is “no evidence of increased severity based on risk of hospitalisation or death”, the UK Health Security Agency (UKHSA) has said.
Preliminary findings from the Wellcome Sanger Institute, one of the research bodies that works with the UKHSA, show potential hotspots for the variant.
It analysed more than 36,000 positive Covid-19 tests from the week to November 13.
In Sheffield 16 per cent of cases analysed were found to be Delta Plus variants, placing it at 109 on the list of local authorities where the variant has been found.
In Doncaster 22.3 per cent of cases analysed turned out to be of the Delta Plus variant.
And in Rotherham and Barnsley it was also higher than Sheffield, at 20.8 per cent and 20.6 per cent respectively.
Torridge in Devon was found to have the highest proportion of Delta Plus cases, at 50.3%, followed by Mid-Devon at 38.1%.
The research is provisional, but gives more localised detail than the official figures published by the UK Health Security Agency.