In central England the mean temperature of 9.0°C in the last week (7th to 13th December) made it the seventh mildest week in the daily CET series since 1772, with an anomaly of +4.3°C.
Of course these are still provisional CET values from the Met Office, but significantly last week was a full 1°C warmer than the same week in 2015, which as you probably know was not only exceptionally mild and the mildest December since 1659, it also the highest anomaly of any month as well. This table is ranked on mean temperature anomalies for all months since 1772, and as you can see December 2015 beat them all into a cocked hat.
Going back to the last week in the CET series and you compare the mean maximum you’ll find it was the joint second mildest week (7th – 13th December) since 1878, with a mean maximum temperature of 11.9°C and +4.3°C anomaly.
I make the CET mean anomaly up to the 13th of December +1.77°C, and I can’t see the remainder of the month being a lot different judging by the available NWP from the American GFS model. It would take a very intense period of severe cold indeed to even reduce the final CET anomaly for this month back to zero.