The Oxford-AstraZeneca vaccine has become the second vaccination against COVID-19 approved for use in the UK, with the first doses due to be given on Monday 4th December.
The second jab, which has been described as a "game changer", has been given the green light by the Medicines and Healthcare products Regulatory Agency (MHRA).
The UK has ordered 100 million doses - enough to vaccinate 50 million people.
This will cover the entire population, when combined with the full order of the Pfizer-BioNTech jab, according to Health Secretary Matt Hancock.
The news comes as millions more people in England are expected to be placed under the toughest tier four restrictions as infections and hospitalisations rise, apparently because of the new and more infections variant.
Scientists believe that both the Pfizer/BioNTech vaccine previously approved and the Oxford/AstraZeneca vaccine will still be effective against the new variant of COVID-19 but it is still very helpful to have two different vaccines available because this significantly reduces the risk that any resistant strain of the disease will be resistant to both vaccines.
The Oxford/AstraZeneca vaccine will also be easier to rollout to GP surgeries and care homes because it does not have to be stored at minus 70 degrees, and instead can be stored in a standard fridge.
The UK strategy to vaccinate as many people as possible as rapidly as possible will make full use of both vaccinations.
Prime Minister Boris Johnson called the development "a triumph" for British science, adding: "We will now move to vaccinate as many people as quickly as possible."
England's chief medical officer Chris Whitty praised the "considerable collective effort that has brought us to this point".
Speaking on BBC Breakfast, Mr Hancock said the development was a "significant moment" in the fight against the virus.
On Tuesday, 53,135 new Covid cases were recorded in the UK - the highest single day rise since mass testing began - as well as 414 more deaths within 28 days of a positive test.
Like the Pfizer/BioNTech vaccine. the Oxford-AstraZeneca vaccine was designed in the first half of 2020, with initial tests on volunteers soon after, and has since been through large-scale clinical trials involving thousands of people.
More than 600,000 people in the UK have been vaccinated with the Pfizer/BioNTech vaccine since Margaret Keenan became the first in the world to be given it outside of a clinical trial. The UK's vaccination programme will deploy both vaccinations from early in the New Year.