Over 90% of new COVID-19 cases in the UK are now the Delta variant.
The variant, first identified in India, took over from the Alpha variant as the most dominant in the UK.
Since last week, the number of cases of Delta variants in the UK has increased by 70% to 42,323.
New PHE research suggests that the Delta variant is associated with an increased risk of household transmission of about 60% compared to the Alpha variant.
And Delta cases are doubling in all parts of the country between 4.5 days and 11.5 days.
In England, 39,061 cases of the Delta variant have now been confirmed, including 2,035 in Scotland, 184 in Wales and 43 in Northern Ireland.
PHE said the sharp increase from 12,341 last week to 42,323 this week was in part due to faster testing times and a faster process to identify cases of the variant.
The latest COVID-19 risk assessment by PHE reports that vaccines are less effective against the Delta variant than the Alpha by 17% after one dose.
But there was little reduction in effectiveness after two, which means that getting a second dose is integral to protecting against the Delta variant.
As of June 7, there had been 42 deaths in England of people confirmed to have the Delta variant and died within 28 days of testing positive.
Of these people, 23 were unvaccinated, seven had received their first dose more than 21 days earlier, and 12 had received their second dose more than 14 days earlier.