Ms Sturgeon says there is a concern that the new strain is driving what appears to be a faster transmission in some hospitals and care homes.

She says the strain is already spreading in the UK and has been seeded in Scotland.

Ms Sturgeon says Scotland has been given a very serious warning.

The bottom line is that if we don't act firmly and decisively now to stop it transmitting, it will take hold here, she says.

The very serious situation in London and Wales will develop here if we don't take action, Ms Sturgeon says.

She says it has the potential to overwhelm the NHS.

The first minister says four weeks ago London's cases were very low and now they are running out of control.

The first minister said most school children in Scotland will be be taught online until at least 18 January.

Nicola Sturgeon announced that school children in Scotland will have a phased return to schooling in the New Year.

The children of key workers will be able to return from 5 January with others from 11 January.

Ms Sturgeon says she does not know how many cases involving the new strain there are in Scotland.

The latest information says there have been 17 cases identified in Scotland through genomic sequencing.

But we must be realistic that is likely to be an understatement, she says.

The first minister has advised against cross-border travel and said increased enforcement was planned as part of new Covid restrictions over the whole festive period.

Most of Scotland faces a return of the toughest level four restrictions from Boxing Day.

They will last for three weeks and apply to all areas except the islands which will be placed in level three.

The planned five-day relaxation of Covid restrictions over the festive period has been cut back to just Christmas Day for the whole of Scotland – with advice to avoid any social mixing.

Ms Sturgeon says cases per 100,000 are about half those in England and about a third those being experienced in Wales.

She says the latest statistics suggest a "broadly stable" position.

However, last week a new variant of the virus was identified.

The first minister says there has been further scientific information on the impact of this new strain.

She says at this stage there is no evidence the new strain causes more severe illness or affects the vaccine.

But there is strong evidence that new strain is spreading more quickly.

It could be up to 70% more transmissible and may be driving the rapidly deteriorating situation in London and Wales.

First Minister Nicola Sturgeon says it is a "serious situation that necessitates action".

She says the information on the new variant of the virus must be taken seriously.

Ms Sturgeon says Scotland has the chance to act on a "preventative" basis.

She says Covid cases had been falling but they have started to rise in parts of the country.

Earlier today, in a tweet, Nicola Sturgeon emphasised that cases were currently at a "lower level in Scotland than [the rest of the] UK".

But she added: "Preventative action may be necessary to stop faster spreading strain taking hold."

The first minister will begin her briefing at 17.30

Nick Triggle
Health Correspondent

The steep increase in the proportion of coronavirus cases linked to this new variant is strong evidence that it is driving transmission.

In London 28% of cases were as a result of this new mutation in mid-November, but that has now increased to more than 60%.

It explains why during the second lockdown cases started increase in London, while in Kent the tier three measures appear to have had little impact in recent weeks.

As chief medical adviser Prof Chris Whitty says this is a bad moment, but there is also some hope.

The prime minister announced 350,000 people had been vaccinated so far in the first two weeks of the programme.

In the coming weeks the number of GP-led vaccination clinics should increase six-fold, while approval of a second vaccine made by Oxford University could pave the way for mass vaccination centres to be set up in sports stadiums and conference centres.

That could see two million people a week being vaccinated.

With 12 million over-65s, in a matter of months this could become to feel very different.

But for now the slog of the pandemic continues - and for many it just got harder.

The whole of Wales is to be placed under lockdown from midnight with festive plans cancelled for all but Christmas Day.

First Minister Mark Drakeford made the announcement after urgent talks with ministers over a new variant of coronavirus.

"We know that 2021 will be a different and a better year. Our economy will recover. Christmas will come again," he said.

Image source, bbc

Prime Minister Boris Johnson announced the changes for England at a Downing Street briefing after scientists said a new coronavirus variant is spreading more rapidly.

"We cannot continue with Christmas as planned," Boris Johnson said.

He told the Downing Street briefing: "I know how disappointing this will be, but we have said throughout this pandemic that we must and we will be guided by the science.

"When the science changes, we must change our response. When the virus changes its methods of attack we must change our method of defence and as your prime minister I sincerely believe there is no alternative open to me."

"We cannot continue with Christmas as planned," Boris Johnson says.

People should not to travel into a tier four area, though support bubbles remain unaffected as do the exemptions for separated parents and their children.

For those in tiers one, two and three, rules allowing up to three households to meet will now be limited to Christmas Day only.

Christmas bubbles for those in tiers one to three will not be able include anyone in tier four.

In tier four, people should not mix with anyone outside their own household, apart from support bubbles.

James Gallagher
Health and science correspondent, BBC News

Image source, SPL

I have one simple rule for making sense of "new variant" or "new strain" coronavirus stories.

Ask: "Has the virus's behaviour changed?"

A mutated virus sounds instinctively scary, but to mutate and change is what viruses do.

Most of the time it is either a meaningless tweak or the virus alters itself in such a way that it gets worse at infecting us and the new variant just dies out.

Occasionally it hits on a new winning formula.

Read more on the new strain

First Minister Nicola Sturgeon is expected to give an update on the Covid rules in Scotland.

It comes after UK Prime Minister Boris Johnson said the planned relaxation of restrictions for between 23 to 27 December would be scrapped for large parts of south-east England and cut to just Christmas Day for the rest of England.

He also announced a new tier four will be introduced in areas including London, Kent, Essex and Bedfordshire.

For the rest of the country, the three household mixing limit has been cut from five days to just Christmas Day.

Earlier today, Ms Sturgeon said more preventative action may be "necessary" to stop a faster-spreading strain of coronavirus taking hold