Are there any geospatial datasets for irrigation in the UK? I've had a look through https://www.ceh.ac.uk/data but there isn't anything for agricultural irrigation in the UK.
It's not spatial, but searching for irrigation on data.gov.uk I found a Defra report about water abstraction for agricultural use (link on this page): https://www.gov.uk/government/statistical-data-sets/agri-environment-indicators
It looks like the underlying data from the EA has not been released yet though - you could ask for it under an EIR request via firstname.lastname@example.org (although, because it hasn't been released as open data it probably means it's not in a single and easily available dataset at the moment)
Quandl has the following free databases, but they are not geospatial. I hope they are a good start though.
World Bank World Development Indicators: https://www.quandl.com/data/WWDI Search for "irrigation UK" in the database and you should see a dataset for % of total agricultural irrigated land in the UK.
Organisation for Economic Co-Operation and Development: https://www.quandl.com/data/OECD Search for "irrigation UK" in the database and you should see datasets for England and Wales showing total freshwater and fresh groundwater irrigation.
Geo3 Data Compendium: https://www.quandl.com/data/GEOCOMP Search for "irrigation UK" in the database and you should see a dataset for Irrigated Land in Great Britain and Northern Ireland.
[Disclosure: I work for Quandl]