Ministers are expected to announce jabs for the over-50s as part of their Covid Winter Plan, after advice from the independent vaccine panel, the JCVI.
BBC political editor Laura Kuenssberg said the booster would be a single dose of the Pfizer vaccine at least six months after a second dose.
The NHS began preparing for the booster programme in July.
But the government has been waiting for recommendations from the JVCI on who should receive the extra doses before announcing more details.
The news on booster jabs comes as the prime minister prepares to set out his plan for managing Covid through the autumn and winter on Tuesday.
Downing Street says he (BJ) will point to vaccines, as the āfirst line of defenceā for tackling the virus, supported by testing, public health advice and surveillance on variants.
In a statement before the announcement, Mr Johnson said while the pandemic āis far from overā, the āphenomenal vaccine programme, new treatments and testingā mean the UK is āable to live with the virus without significant restrictions on our freedomsā.
And he said he will lay out a strategy for the months ahead āwhen the virus has a natural advantage, to protect the gains we have madeā.
Boris Johnsonās Covid Winter Plan for England is expected to focus on contingency measures that would be brought in if the NHS was at risk of becoming overwhelmed due to the virus.
Earlier, the PM confirmed the booster programme would be āgoing aheadā and had āalready been approvedā, but without further detail.
Mr Johnson was also pushed on whether future lockdowns were being considered, but he told reporters: āI will be setting out a lot more tomorrow, Iāll be giving a full update on the plans in the autumn and winter.ā
No mention that Professor Dame Sarah Gilbert, one of the leading figures in the development of the Oxford Astrazeneca vaccine saying that not everybody needs a booster, so it will be interesting to hear who actually gets the booster.
Sajid Javid told the Commons the government had accepted advice from the the JCVI that around 30 million people should be offered a third dose. This includes over-50s, younger adults with health conditions and frontline health and social care workers. The Pfizer jab is recommended and it should be given at least six months after the second dose.
It is part of the governmentās plan for managing Covid through the autumn and winter.
The recommendation from the JCVI (Joint Committee on Vaccination and Immunisation) comes amid concern about waning immunity. There are some signs protection offered by the vaccine may start dropping off several months after the second dose - with the most vulnerable groups most at risk of this. The JCVI said it was still unclear exactly how much protection does slip, but it wanted to take a precautionary approach and ensure the most vulnerable people maintain high levels of protection.
Saves them having to destroy another 1m doses I suppose.
One of the leading scientists behind the Oxford vaccine for Covid-19 has said she does not support a widespread booster jab campaign in the UK as immunity among fully vaccinated people is ālasting wellā Prof Dame Sarah Gilbert, who developed the Oxford/AstraZeneca jab, one of the most widely used Covid vaccines in the world, suggested extra doses should be directed to countries with a low rate of vaccination.
Britain promised to donate 80m does to poorer countries but so far has only donated 5m.
If we want to visit and trade with these countries then they need to be vaccinated.
Given that thereās 30,000 people a day (1,000,000 a month) tested positive for COVID I would suggest that many elderly and vulnerable people would feel happier with a booster if, as it seems, they have to mix with so many potential carriers ā¦
Since hundreds of thousands of UK citizens have died or been incapacitated by BJās previous vacillations it makes sense for the government , this time, to be more careful than less ā¦
Downing Street press conference due to start at 15:30 BST.
The prime minister will present the governmentās Covid autumn and winter plan.
Boris Johnson will then take questions alongside Chief Scientific Advisor Sir Patrick Vallance and Englandās Chief Medical Officer, Professor Chris Whitty.
But this winter is āincreasingly unlikely to reach the peak of the January 2021 waveā, says SAGE
JCVI recommends starting booster campaign - with over-50s offered a Pfizer dose six months after their second jab or a half dose of Moderna
COVID-19 vaccine available for 12 to 15-year-olds in England from next week - and child can have jab without consent from parents if deemed ācompetentā
Fully vaccinated people made up just 1% of coronavirus deaths in England in first half of 2021, figures show
BJās banking on the vaccines ā¦ otherwise itās another winter lockdown ā¦
Just had a text from our surgery, saying that they are ready for appointments for both the Covid booster jab and the Flu jab. Said that both could be taken together. Also that they had enough supplies for all patients. Me and the wife are booked in for October 20th.
As I am in Scotland things are done differently. Last year I had to stand in a long queue in the street with other older folk waiting to get our flue jabs and this in November
The covid jabs I had to go to my local vaccination centre, I say local but it was a two bus journey to get there.
My health board could not organise a piss up in a brewery.
Research suggested that mixing vaccines produces a stronger immune response and can provide better immunity against new strains of Covid.
Since the Delta variant is still infecting so many Iām guessing that in light of that research they think it a better option than a same-type booster.
There was an israel study that people who had received MRNA vaccines benefited from an MRNA booster. For AZ itās going to be MRNA boosters. So Iām not sure whether they will be giving AZ(viral vector) boosters to MRNA vaccinated unless they run out of MRNA.
The trouble with mix and match, if you run into trouble later on, you, as in an individual will have no idea what the source was, a couple of years down the line, the data analysts will have an idea, but, you wonāt.
