Boris Johnson has announced tighter Covid measures after two cases of the Omicron variant were discovered in the UK.

Face coverings will again be mandatory in shops and on public transport, while everyone entering the UK will need to self-isolate until they receive a negative PCR test, the Prime Minister announced at a press briefing this evening.

Mr Johnson also announced that the UK's Covid booster jab scheme will be ramped up, while anyone in contact with someone who tests positive for the Omicron strain must isolate for 10 days.

His announcement comes as two people in Essex and Nottingham tested positive for the new strain, which has also been found in countries including South Africa, Botswana, Belgium, Hong Kong and Israel.

The Prime Minister said it appears Omicron "spreads very rapidly, and can be spread between people who are double-vaccinated".

He went on: "We need to take targeted and proportionate measures now...to buy time for our scientists to understand exactly what we are dealing with.

"We're not going to stop people travelling, but we will require anyone who enters the UK to take a PCR test by the end of the second day after their arrival, and to self-isolate until they have a negative result."

He added the government will also now require all contacts of those who test positive with a suspected case of Omicron "to self-isolate for 10 days, regardless of your vaccination status".

"We will also go further in asking all of you to help contain the spread of this variant by tightening up the rules on face coverings in shops and on public transport," he added.

"And most importantly we need to bolster our protections against this new variant.

"We don't yet exactly know how effective our vaccinations will be against Omicron, but we have good reasons for believing they will provide at least some measure of protection.

"If you're boosted, your response is likely to be stronger, so it's more vital than ever that people get their jabs and we get those boosters into arms as fast as possible.

"So from today, we're going to boost the booster campaign over the next three weeks and now we're looking to go further.

The Health Secretary has asked the Joint Committee on Vaccination and Immunisation to consider giving boosters to as wide a group as possible, as well as reducing the gap between second doses and boosters.

Mr Johnson added that the measures being rolled out today were "temporary and precautionary", and will be reviewed in three weeks.

"At that point we should have much greater information about the continuing effectiveness of our vaccines," he said.

Regarding the upcoming Christmas period, he added: "I'm absolutely confident this Christmas will be considerably better than last Christmas."