UK's long-standing weather records have been smashed by a stormy, yet warm December, the Met Office said.
Scotland, Wales and the north-west of England all had the wettest December in more than a century, it said, citing early figures.
A UK mean temperature of 8C broke records too and would have felt more like a day in April or May.
The Met Office said storms Desmond, Eva and, most recently, Frank were behind the record rainfall, while a humid south-westerly airflow kept it warm.
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Wales has only seen more rain fall in a single month once than it did in December 2015 - in November 1929.
Central and southern England escaped the worst of it, with rainfall figures much closer to average.
The Met Office said that, until last week, the year might have looked unremarkable with a cool spring and a cool, damp summer offset by a mild end to the year.
However, this week's rainfall will make 2015 one of the top 10 wettest years since 1910, when the Met Office's digitised records begin. The wettest was 2000, when 1,337mm of rain fell.
On Christmas Eve, gales and heavy rain from Storm Eva flooded parts of the north-west of England, Scotland and north Wales.
And in recent days, Scotland, Northern Ireland and northern England have borne the brunt of Storm Frank.