Government officials and scientific advisers believe that the danger posed by the Omicron variant may not be clear until January, potentially allowing weeks of intense mixing while the variant spreads.
Across Westminster, invitations to Christmas drinks are landing in embossed envelopes or on WhatsApp groups. Departmental staff parties are set to take place, as well as a reception for journalists with Rishi Sunak at No 11. Even Keir Starmer and Rachel Reeves are hosting a joint bash.
However, minutes for the Scientific Advisory Group for Emergencies (Sage) suggest there is deep concern about the threat from the new variant, particularly its transmissibility. Though there is a wariness about overreacting, one government scientific adviser said Downing Street was â€œputting all its eggs in one basketâ€ by focusing its efforts on the booster vaccine drive.
â€œIt should be a balance between social mixing and immunity. That will affect how quickly it spreads,â€ the adviser said. â€œAt the moment we are not really doing anything to reduce mixing. Itâ€™s disruptive and itâ€™s damaging to the economy, but at the very least we could encourage people to think about their contacts.â€
Some senior Sage scientists have made the case privately that the additional precaution of home working should be taken in the run-up to Christmas and that the government should start to suggest that people take sensible steps to minimise social contact in the days before seeing loved ones.
â€œWorking from home is substantially less intrusive as an intervention. If you can easily do your job from home until Christmas, to me that seems a very proportionate thing to do right now,â€ one Sage adviser said.
â€œWe may wait till next year to see an exponential increase and then introduce plan B. And then that doesnâ€™t work and we end up having to do more intense things. Itâ€™s undoubtedly a very difficult judgment.â€
That advice has so far not been taken, and ministers who have suggested that people exercise their personal judgment over Christmas party participation have been slapped down by No 10.
After the work and pensions secretary, Therese Coffey, counselled caution over â€œsnoggingâ€ under the mistletoe, the health secretary, Sajid Javid, intervened on Thursday to insist that â€œitâ€™s got nothing to do with the government who you kissâ€.
Government sources have also firmly denied that there has been any consideration of a short â€œcircuit breakâ€ lockdown in order to allow more mixing over Christmas. â€œItâ€™s totally wrong to suggest that has been considered,â€ a spokesperson said.
However, one senior health source said that although intensive mixing often occurrs in the run-up to Christmas, people would be expected to decrease that over Christmas itself. â€œThe Christmas holidays may act as a form of circuit breaker â€“ people stay at home in smaller groups, kids are off school after a period of lots of mixing. That will help,â€ the source said.
Another Sage scientist said it would be hard to make the case in the early weeks for a crackdown on social contact because the figures would look absurdly low in relation to the daily infection rates that Britons have come to expect.
â€œThe first part of the curve looks flat and then it suddenly takes off and the exponential nature becomes more obvious. I donâ€™t think we will reach that point before Christmas. We will reach it in the first quarter of next year.â€
Ministers acknowledge that the current figures for Omicron in the UK may be more than two weeks old and vastly underestimate the true picture.
â€œWe are talking about big underestimates. The sequencing is always a week or more behind. We are looking at the numbers we had a week or two ago and itâ€™s an underestimate of that,â€ one official said.
The rapid-response restrictions, which include additional measures for self-isolation of contacts as well as mask wearing, will be reviewed in three weeks. Some scientists said the data from South Africa would be clearer by then, but the implications for the UK would still be very uncertain.
â€œIf we see the exponential increase in cases and hospitalisations are staying flat, that would be positive, but the population [in South Africa] is much younger; much of the early circulation is the young adult population. Itâ€™s not necessarily completely reassuring if you didnâ€™t see that increase,â€ one government scientist said.
â€œUltimately, the only thing that really tells us this, is the real-world data. It would take us a month, even with our extremely good data, to have a good understanding of what is really happening. Unfortunately we get that detail once itâ€™s widespread.â€
No 10 believes the actions over the past week showed a recognition of where ministers needed to move quickly, without an overreaction when evidence of the threat is still unknown.
â€œBecause of the uncertainty, we have acted swiftly and decisively but also in a proportionate way,â€ one senior adviser said. â€œThere was broad recognition on the importance of working at speed. That has been borne out by the fact we identified our first confirmed case very shortly after announcing initial border measures.
â€œOur whole approach has been to act swiftly to buy time and then make good use of that time to get a better understanding of this variant whilst building up our defences against the potential threat. Thatâ€™s why we are putting the booster programme on steroids.â€
Despite widespread support for extra precautions at the border and additional mask wearing, there is no big push from the public for Johnson to go further.
Most adults in England are unwilling to return to full lockdown rules, according to the latest polling from YouGov, which found 68% were against closing pubs and 56% were against the return of limited numbers at gatherings.
However, the polling has not moved significantly since the end of the roadmap in July, suggesting the public are sanguine or jaded about the new threat.
Emerging information from South Africa could start to shift public opinion. One Sage adviser called the latest findings from South Africa â€œextraordinaryâ€, with new cases appearing to have doubled within 24 hours, and the variant reinfecting people at three times the rate of previous strains.
â€œIf you have a much more transmissible strain then itâ€™s highly likely you will get a big wave of infections, and even if the fatality rate is the same, then you will see a big increase in hospitalisations and deaths,â€ a government scientific adviser said.
â€œEven reductions of 10-20% in vaccine effectiveness against severe disease could lead to very substantial problems.â€