There are now 4,558 confirmed cases and further 13,688 suspected cases, government data shows.
Suspected cases are found when scientists analyse the virus looking for a DNA marker called the S-gene, which is present in Delta cases but missing in Omicron and Alpha.
Once identified, swabs showing the so-called ‘S-gene dropout’ can then be sent for definitive testing for Omicron.
This means more likely Omicron cases can be identified.
And the data shows how London has become the Omicron capital in England, with 14 boroughs in the top 20 council areas for suspected case numbers.
Southwark has the most suspected Omicron cases in both the capital and England.
The south London borough has 219 confirmed cases and a further 1,028 suspected cases.
Neighbouring Lambeth has the second highest number of likely Omicron cases in both London and England, with 411 confirmed and an additional 692 suspected.
And another south London borough, Lewisham, is third in both England and London.
It has 161 confirmed cases and 930 suspected cases.
Greenwich, Enfield and Wandsworth were ranked sixth, seventh and eighth for highest number of likely Omicron cases across England.
Each had 919, 859 and 814 suspected cases respectively.
And Newham, Waltham Forest, Tower Hamlets, Brent, Haringey, Croydon, Hackney and City of London and Bexley were all in the top 20 Omicron areas across England.
Speaking alongside the prime minister Boris Johnson and NHS England primary care director Dr Nikita Kanani on Wednesday, December 15, he also said Covid rates were beginning to increase, “in some places” and especially in the London area.
He said: “When it comes to hospitalisations, this always reflects where we were two or more weeks ago and therefore the rates have remained reasonably flat over quite a while.
“[It is] reflecting where we’ve been with Delta over the last several weeks, so rates are currently flat but they are beginning to increase in some places particularly in London.”
Prof Whitty said data on deaths did not yet reflect infections from the spread of Omicron, and added: “Deaths of course reflect what happened even earlier in time and those are still - if anything - going down very slightly.
“In London now the majority of cases are going to be Omicron and therefore that is going to be where we will be.
“From the time we get to probably Christmas onwards, I would expect most cases going to hospital to start being Omicron cases.”
The government is urging the public to take up their booster jabs, with the rollout expanded to all over-18s and over-30s encouraged to book appointments.