A bit more on low maxima in London. According to this page on Trevor
Harley's excellent website:

http://www.personal.dundee.ac.uk/~ta...in_january.htm

the three coldest January days in London on record are, in chronological
order:

8th January, 1841: max of -8.3C at Greenwich
4th January, 1867: max of -8.3C at Camden Square
12th January, 1987: max of "reportedly" -9.1C at Warlingham and -8C
"across large parts of the south"

Too much notice should not be taken of the tenths of a degree in the
first two values, as I suspect that they are converted from values
originally read to the nearest whole degree Fahrenheit.

Obviously 1740 is likely to have produced at least one colder day, as
may some other early winters, but accurate instrumental readings are
lacking.
--
John Hall
"One half of the world cannot understand
the pleasures of the other."
From "Emma" by Jane Austen (1775-1817)