Here are links to websites which will give you verified data on a range of issues in the UK to help legitimise your accountability research and identify evidence to support your work:
The Office for National Statistics will have information and data on almost any issue you search for, all you need to do is search using some keywords (‘Atmospheric Emissions’).
Search for any topic on the official UK Government website to research official definitions of topics (e.g. Female Genital Mutilation) and any government action on this, as well as statistics which concern these issues. If you don’t have a specific advocacy issue, but have a general theme in mind, you could take a look at the official website for each ministry and department, where you’ll be able to see a list published data reports. For example, you can find statistics on crime and prosecution at the Ministry of Justice statistics page.
You can use the NHS website to search for in-depth definitions of medical issues.
Many non-Governmental organisations / charities in the UK which work on your interested topic are likely to have collected their own data on your advocacy topic. You can easily search online to find these charities and look on their websites to see any of their published reports.