All travelers will need to take the test, amid warnings that the time between infection and contagiousness may be shorter with the latest strain.
Health Secretary Sajid Javid warned the variant was spreading within communities, rather than just being linked to international travel.
The decision on pre-departure testing follows calls from Labor to implement the process.
This means that anyone traveling to the UK from countries not on the Red List will have to take a pre-departure test no more than 48 hours before leaving, regardless of their vaccination status.
Anyone who returns a positive test result will not be permitted to travel.
Scotland and Wales have said they will implement similar measures.
However, the requirement has been met with anger and dismay across the travel industry.
On Monday, Mr Javid said: “The Omicron variant continues to spread here and around the world.
“According to the latest data, there are now 261 confirmed cases in England, 71 in Scotland and four in Wales, bringing the total number of confirmed cases in the UK to 336.
“This includes cases unrelated to international travel. We can therefore conclude that there is now community transmission in several regions of England. “
He said the government cannot “say for sure” whether Omicron will escape Covid vaccines, or how severe illness will be caused.
He told MPs: “We are learning all the time about this new variant.
“A recent analysis from the UK Health Security Agency suggests that the window between infection and infectivity may be shorter for the Omicron variant than for the Delta variant, but we do not yet have a complete picture of whether Omicron causes more serious illness or how it interacts with vaccines.
“We can’t say for sure at this point if Omicron has the potential to get us out of our way to recovery. “
He added: “We leave nothing to chance. Our strategy is to save time and strengthen our defenses while our world-renowned scientists assess this new variant and what it means for our fight against Covid-19. “
Mr Javid said that of the cases identified so far, none have resulted in hospitalization and the measures are temporary, acknowledging they will cause disruption.
“We are taking this step early now so that we do not have to take more severe measures later, and so that we can take every opportunity to prevent more cases from arriving in our country,” he said. he declares.
Labor leader Sir Keir Starmer, meanwhile, said the government must now do ‘everything it can’ to lower the price of Covid-19 pre-departure testing.
He said: “I wish the government had acted faster. As always, they are lagging behind. As soon as we saw the scientific evidence that there should be pre-departure testing, we called on the government to do it last week. The government has delayed, as it always does.
“They’ve done it now, that’s a good thing. But the government must move forward instead of being late. “
He added: “I also want to see the government doing everything possible to bring down the price of these tests because a lot of people… (are) really hammered by prices that cannot be justified. “
Those arriving from countries on the red list of travel restrictions will have to quarantine themselves in hotels.
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