UK Office of Fair Trading: http://www.oft.gov.uk
At this site you can find information on how firms must comply with legislation enforced by the OFT, and follow the progress of investigations and action taken.

Trading Standards Central: http://www.tradingstandards.gov.uk/
Contains information about legislation that affects firm's pricing decisions.

Institute of Economic Affairs: http://www.iea.org.uk
The IEA is the UK's original free-market think-tank, founded in 1955. The IEA's goal is to explain free-market ideas to the public, including politicians, students, journalists, businessmen, academics and anyone interested in public policy.

Office for National Statistics: http://www.statistics.gov.uk/
The UK government's statistical service includes data on price trends.

The Institute for Fiscal Studies: http://www.ifs.org.uk/
IFS is an independent research organization, which provides high quality economic analysis of public policy. The IFS home page provides links to analysis of topical economic issues, government budgets, IFS surveys and other online economics and social sciences resources.