The Health Secretary will tell MPs how the Government is responding to the new Omicron variant first detected in South Africa. So far three cases have been confirmed in the UK.
Scientists are frantically analysing the new strain to understand more about the mutation, with fears it could be more transmissible and have some resistance to the vaccines currently being rolled out around the world.
At a hastily arranged televised press conference on Saturday, Prime Minister Boris Johnson said extra measures were being reintroduced to help slow the spread of the variant in the UK.
Face coverings will once again become compulsory on public transport and in shops from Tuesday, while isolation rules will return for international arrivals until they receive a negative PCR test.
Close contacts of positive Omicron cases were being ordered to isolate for 10 days even if they have been double jabbed.
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The Health Secretary will give more details about the new restrictions this afternoon.
He is due to address the Commons at 3.30pm.
The measures being introduced tomorrow will be reviewed in three weeks, with ministers hinting extra precautions could be introduced ahead of the festive break.
Restrictions being reimposed stop short of the full coronavirus Plan B set out by Mr Johnson earlier this year, with no work-from-home guidance of imposing of vaccine passports.
If the Omicron variant spreads rapidly across the UK and risks an increased number of hospitalisations and deaths, ministers may resort to the full back up plan.
Imperial College immunologist Peter Openshaw has today warned in a newspaper article that it would be a few weeks before "we can be confident about our Christmas plans".
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Speaking to the media over the weekend, Mr Javid admitted it "would be irresponsible to make guarantees" that Britons will not be forced to drastically change their Christmas plans.
However, he said he believed it would still be a "great Christmas" and people should not worry at this time.
He told Sky News yesterday: "I think people should continue with their plans as normal for Christmas, I think it's going to be a great Christmas."
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Addressing the public from Downing Street on Saturday, the Prime Minister said the measures currently being imposed were "targeted and proportionate".
He said: "Our scientists are learning more hour by hour, and it does appear that Omicron spreads very rapidly, and can be spread between people who are double vaccinated.
"There is also a very extensive mutation which means it diverges quite significantly from previous configurations of the virus, and as result, it might – at least in part – reduce the protection of our vaccines over time.
"So we need to take targeted and proportionate measures now as a precaution while we find out more."
He added: "I very much hope that we will find that we continue to be in a strong position, and we can lift these measures again.
"But right now this is the responsible course of action, to slow down the seeding and the spread of this new variant, and to maximise our defences so we protect the gains we have worked so hard for and so that we can continue to save lives."
As well as Mr Javid's announcement today, it is expected the Joint Committee on Vaccination and Immunisation (JCVI) will today recommend expanding the boost jabs programme to all adults and cutting the gap before a third dose.
JCVI deputy chairman Professor Anthony Harnden said extending the age range for boosters and reducing the gap between second and third doses was "a sensible strategy".