As of 4 a.m. on Tuesday it is now a requirement for passengers entering the UK to take a COVID-19 test before their journey.

The measures are part of a nationwide strategy to mitigate the spread of the new Omicron variant, which was first discovered in southern Africa.

Scientists are divided over how effective these measures might be but lawmakers were heavily criticized when the Delta variant spread during the summer and don't want to be caught out again.

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It's a decision the UK travel industry says will deliver a hammer blow to the sector, and it's true that across Europe and the UK there are certainly signs that holidaymakers are having second thoughts about their winter vacations.

But that's not necessarily connected to the prospect of a pre-arrival testing program.

Health Secretary Sajid Javid reiterated the government's determination in the House of Commons. "Anyone traveling to the UK from countries that are not on the red list must also show proof of a negative PCR or lateral flow test," he said. "This applies to any vaccinated travelers, so whether you're vaccinated or unvaccinated, anyone aged 12 or above."

So all travelers entering the UK must do so carrying proof of a negative COVID-19 test taken before their journey.

They already have to take a PCR test on their return and any contact with a suspected Omicron case means self-isolation for 10 days.

However, the government has confirmed, since its decision to mandate pre-travel tests, that the new variant is now spreading within communities inside England.

There are more than 330 recorded cases of Omicron in the UK so far and scientists are now convinced it will take over Delta as the dominant strain within a matter of months, possibly weeks.

Face masks are now compulsory again on public transport and in shops but other than that, government measures are not going much further.

There are reports of companies reintroducing working from home and canceling Christmas parties but that remains an individual choice.

For travelers then, the impact is most significant. It's not clear yet how much the individual travel operations like the airlines will be affected.

And it's still not clear what the health implications are with the new strain. It's certainly very infectious, but its effectiveness against vaccines will take longer to figure out.