Researchers analysing positive Covid tests from the week to March 12 found 84 per cent were the subvariant, branded “Stealth Omicron”.
That is up from 37 per cent only a fortnight before.
The analysis by the Wellcome Sanger Institute comes as coronavirus infections and hospitalisations surge across the UK, with researchers saying the contagious subvariant is a key reason for the spike.
Stealth Omicron got its nickname because it is more difficult to differentiate from Delta than the original Omicron variant, BA.1.
It is also more contagious but early studies seem to show no greater risk of hospitalisation for an infected person, according to the UK Health Security Agency (UKHSA).
A spokesperson for the UKHSA said: “Omicron BA.2 is now the dominant variant in the UK, and has a significant growth advantage over Omicron BA.1.
“UKHSA continues to monitor all available data related to Covid-19 variants as a matter of routine, both in the UK and internationally.
“Vaccination provides a high level of protection against severe illness and it's important that everyone has had their latest dose.
“We can all help reduce transmission by wearing a face covering in crowded or enclosed spaces, washing hands regularly and keeping rooms well ventilated.”
The Wellcome Sanger Institute analysed more than 41,000 Covid tests from the week ending March 12, taken from every part of England.
Regionally, London had the greatest proportion of samples testing positive for Stealth Omicron.