Here are 2 good resources to find BIDs across the UK.
The Institute of Place Management has a good interactive BID map. Clicking on an icon will take you through to the details of that BID.
British BIDs has a BID INDEX, which features all of the developing BIDs, current BIDs and failed BIDs to date. Simply enter the BID or town name, and you can access the BID website address.