Travellers heading to the UK will now have to take a Covid test before their departure in an effort to limit spread of the virus, the government has said.
Health Secretary Sajid Javid said the tightened requirements would come into force from 04:00 GMT on Tuesday.
Everyone aged 12 and over will be required to take a pre-departure test a maximum of 48 hours before leaving.
Currently people only need to self-isolate until they test negative within two days of arriving.
Nigeria will be added from Monday to the red list of countries from where people arriving must quarantine in a hotel for 10 days, Mr Javid also confirmed.
The health secretary said the government’s strategy since the discovery of the Omicron variant had been to “buy time” to assess and to “put in place protective measures”, adding: “We’ve always said that we would act swiftly should new data require it.”
The Department of Health and Social Care later said 21 Omicron cases linked to Nigerian travel had been discovered in recent days.
Mr Javid said this number was growing and Nigeria was now second only to South Africa in terms of linked cases to Omicron.
He called on people to get a booster vaccine when called to do so by the NHS, describing vaccinations as the country’s “first line of defence” against coronavirus.
A further 26 Omicron cases – of which 25 were recorded in England and one in Scotland – were confirmed in the UK on Saturday.
Those cases took the total for England to 129. Scotland has so far recorded 30 cases while one case was identified in Wales, bringing the total for the UK as a whole to 160.
The Scottish and Welsh governments have confirmed they will also bring in the updated measures for travellers following the assessment of the UK Health Security Agency.
The moves come after pressure on the UK government to tighten the policy on overseas arrivals.
Last week the government’s scientific advisory body Sage said pre-departure tests for those arriving in the UK would be valuable, in the leaked minutes of a meeting seen by the BBC.
Following the latest announcement Labour’s shadow health secretary Wes Streeting called for further action and for the number of booster jabs given to be increased to 500,000 per day.
In a tweet he said: “Finally the health secretary accepts Labour’s call for pre-departure tests, but why up to 48 hours before flight?”