Officials designated the strain, officially called AY.4.2, a ‘variant under investigation’ on October 20.
They have said it may spread more easily than the standard Delta strain, but there is no evidence that it causes more serious illness.
There is also no evidence that the three Covid vaccines used in the UK are any less effective against the new strain.
Preliminary findings from the Wellcome Sanger Institute, one of the research bodies that works with the UK Health Security Agency (UKHSA), show potential hotspots.
It analysed more than 26,000 positive Covid-19 tests from the week to October 30.
These are the areas of England which saw the highest proportion of Delta Plus samples.