If you need a full historic supply of a single site, or for data more than 12 months old, you would need to make a request for an offline supply via firstname.lastname@example.org
The Rainfall API currently provides access to data for the last month.
Historic rainfall data for the past 12 months is available to download from our archive in csv format: http://environment.data.gov.uk/flood-monitoring/archive
To download the data as a csv, simply highlight the top row and select the filter button:
You can filter the results to the station or area of interest.
Please note this is unvalidated data and could potentially contain errors due to faulty instruments or on-site maintenance.