There were 336 Omicron cases confirmed in the UK as of December 6, according to the UKHSA.
The individuals who have tested positive for the Covid strain and those who are in close contact with them are all isolating.
The UKHSA has identified cases in the East Midlands, East of England, London, North East, North West, South East, South West and West Midlands.
There are 71 confirmed cases in Scotland.
Four cases have been identified in Wales and no cases have been confirmed in Northern Ireland so far.
Covid guidelines implemented on November 30 remain in force. These include wearing a face covering in shops and on public transport, unless exempt. Those who do not comply with the rules are faced with a £200 fine.
Visitors and pupils in year seven and above should also wear masks in communal areas of universities, colleges and schools.
When travelling to England from abroad, holidaymakers and travellers must take a PCR test before the end of day two following their arrival and self-isolate until they get a negative test result, even if they are fully vaccinated.
If in contact with someone with the Omicron variant, you must self-isolate for 10 days, no matter your age or vaccination status.
All eligible adults in England aged 18 and over will be offered a Covid-19 booster jab by the end of January.
According to the independent experts at the Joint Committee for Vaccination and Immunisation (JCVI), eligible adults over 18 will be able to book their booster vaccine from three months after their second dose.
Vaccines minister, Maggie Throup, said: “It’s truly a testament to the brilliant work of our NHS and its volunteers that over 18 million booster jabs have now been provided across the UK.
“We are now asking them to undertake another big and critical step up in the programme, with millions more boosters being offered over the next few months.
“Getting your jab is the most important thing you can do ahead of Christmas to keep yourself safe from the virus - do not delay in booking as soon as you’re eligible.”
NHS chief executive, Amanda Pritchard, said: “The NHS Covid vaccination programme was already in its most complex phase and staff are now working at breakneck speed to respond to the new variant and the expansion of the booster programme, which has already administered more than 15 million doses across England.
“The NHS will roll out this latest phase of the programme to the most vulnerable first, offering the booster jab to those over 40 who would have previously had to wait six months, before moving on to younger age groups.
There is no need to contact the NHS, we will contact you when it is your turn to book. The NHS is working hard to ensure every adult who is eligible is offered a chance to book in for their booster by the end of January.”