Going to move a congested 5 frame nuc in the morning
As usual, we have some jumping the gun.
No mention of why/how they are congested, in the OP. Removing one frame of stores and replacing with foundation could have been ther simplest answer. Adding three frames of foundation is excessive - two, at most, and possibly only one in the present weather conditions.
Very little is irrelevant at the present time. Everything needs to be taken into account.
Minus three at night is unseasonable (yes, the odd frost is expected, but not usually worse than minus one) and the cold night temperatures are following days with little foraging opportunity.
Those living in London may well benefit from the warmer night temperatures within the city, but those out in the real world are not advised to blindly follow 'London practice' without considering their own set of conditions. Beekeepers need to think, not just follow the loudest bleat.