The Met Office has recently published historical data based on 1km square resolution as an addition to its previous data based on 5 and 25km squares.

http://catalogue.ceda.ac.uk/uuid/2a62652a4fe6412693123dd6328f6dc8

Data is available on a daily basis for rainfall (1891-2017) and Maximum/Minimum Temperature (1960-2017) with many other variables such as Mean Temperature, Sunshine Hours, Wind Speed, MSLP, Snow Lying and others available as Monthly data at 1km res.

As samples, these graphics look at 3 notable events in UK weather history:

SE Rainfall 14-15 September 1968
SE Heat Wave 10 August 2003
UK Cold Day 12 January 1987

For the 1st two, both the 1 and 5km res graphics are shown below to demonstrate the increased resolution particularly for local analysis

Data volumes are extremely high (1 day for the UK contains about 250,000 data points for each variable) and unlike the lower res data cannot be obtained in ASCII text format. It is held as NETCDF (.nc) data and unfortunately requires specialist software to decode

(clickable)