Can Boris Johnson's new Covid measures slow the spread of Omicron and keep anti-lockdown MPs onside?
The threat of a new Covid variant has always been there, but it couldn't have come at a worse time with colder weather across the UK and millions of people planning to criss-cross the country next month for Christmas celebrations.
Both of these facts mean socialising indoors will become more common and that's exactly the kind of conditions coronavirus thrives in.
Speaking at a Downing Street press conference on Saturday, the prime minister said this Christmas will be better than last year and there is a real determination that, after cancelling Christmas for millions and shortening it for millions more last year, we will have much more freedom this year.
Watch the prime minister's press conference in full
However, the new rules are a reminder of just how quickly things can change.
The challenge for the government is whether the restrictions announced today can stem the flow of the new Omicron variant coming into the country and stop the spread from the cases already here.
Boris Johnson has often been criticised for not acting quickly enough against the first wave of Covid and the ensuing variants.
Downing Street is looking to avoid that criticism this time round, especially with the return of the red travel list for 10 southern African countries and the more reliable PCR tests for passengers returning from other countries. The aim of these changes is to stop (or at least limit) importing more cases into the UK.
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The reality is the new rules for England announced today are only a fairly small tweak to the ones we have been used to for a few months, so most MPs won't have a problem with them, but should the PM need to restrict our lives further then he will certainly start to face increasing opposition from some on the Conservative backbenchers who do not believe lockdowns are appropriate or needed.
The prime minister has stopped short of introducing the full 'plan B', so if more restrictions need to be imposed, this is likely where he'll start - that would mean 'work from home' guidance and vaccine passports for some venues and events.Labour is already putting pressure on the PM to go further and introduce all of 'plan B' now, arguing that work from home instructions and introducing Covid certificates are an inexpensive way of helping to control the virus.
Despite these calls I think the prime minister will resist them for as long as possible, hoping that the latest rule changes will be enough to stem the infection rates of the new variant.
The fact the Omicron variant is now in the country means there'll be more cases. The challenge is to slow that spread whilst it is investigated.
The key question for scientists is what protection the existing vaccines give against the variant, whilst other scientists race to adapt vaccines to fight Omicron specifically.