UK deliveries seem to take quite long for me even when it's not busy Christmas season.
The general public cannot understand the volumes of packages that must be passing through the border, the couriers etc.
Best thing is to hold of on shipping stuff if you can wait or get it at a brick and mortar store.
Ensure your address etc is correct and keep tracking everyday and a call in if necessary.
Make sure your packages do not require signatures so they can leave it at your door if you are not home to receive it.
Keep in mind it's the season for professional thieves to stake out your home for package deliveries as well.