The government recommends that local authorities publish expenditure over £500 and all expenditure made on purchasing cards. As of January 2014 and in line with our commitment to openness and transparency we will now be publishing ALL transactions (note; areas may be redacted as they may be commercially sensitive or there may be data protection issues).
Local Government Transparency Code 2015
This is a key dataset which the government wants local authorities to publish.
https://www.gov.uk/government/publications/local-government-transparency-code-2015