Boffins at the Wellcome Sanger Institute, part of the Covid-19 Genomics UK Consortium, have been analysing a sample of Covid tests from across the country to work out what variant each is.
Scientists have said Delta Plus carries two characteristic mutations in the spike - Y145H and A222V - both of which have been found in other coronavirus lineages since the start of the pandemic.
In London, around one in 10 positive cases belong to Delta Plus in the week to October 9 - according to the latest Wellcome Sangar Institute figures.
Overall, 2,194 tests from London were genome sequenced with 212 coming back as Delta Plus.
Not all tests were checked, so the figures do not show the total number of people with the new strain, but the variant’s positivity rate.
Islington had the highest percentage of Delta Plus positives, with 26% of sequenced test belonging to the new variant.
However the Wellcome Sangar Institute only tested 19 cases from the north London borough, with five belonging to Delta Plus.
Kensington and Chelsea had the second highest Delta Plus positivity rate, with six of 33 tests coming back as Delta Plus - or 18%.
While Westminster had the third highest rate, at 16%.
Tower Hamlets has the fourth highest proportion of positive Delta Plus cases, at 14%.
While Harrow, Hammersmith and Fulham, Waltham Forest, Richmond, Barnet and Hackney and the City all had 13% of Delta Plus positives.
Barnet had the highest number of new variant cases at 17, but it also had a higher number of tests sequenced that any other borough at 136.
Croydon had the lowest proportion of Delta Plus cases, with just four out of 116 tests checked - or 3%.
Southwark and Barking and Dagenham both had 4% of their positive cases come back as the new variant, while Havering and Newham both had 5%.
The Government has renewed its calls for people to get vaccinated against Covid-19 after warning of the potential threat of future variants.
Health Secretary Sajid Javid has said that new variants are being identified “all the time” and, at the moment, Delta Plus poses no greater threat than any other variant.
But Mr Javid urged people to get vaccinated against Covid-19, and take up the offer of a booster dose, to help keep infections under control after warning cases could rise to 100,000 per day this winter.
He said: “While there’s no reason to believe at this point that AY.4.2 poses a greater threat, the next variant, or the one after that, might do.
“So we need to be ready for what lies around the corner. This means our ongoing programme of booster jabs is so important, and this winter we’re prioritising those most in need.”