You asked
Please advise as to the average cost per prosecution in the UK.
We said
Thank you for your enquiry.
Unfortunately we are unable to be of assistance on this matter. Data relating to court proceedings and their associated costs is not held by us. The Crown Prosecution Service do hold data on the above and may be able to assist you further on this matter. Their most recent publication (https://www.cps.gov.uk/legal-guidance/costs) provides some relevant information and associated caveats (Annex 1).
Their contact details are as follows: IMU@cps.gov.uk
If you would like any crime related information in the future, you can email CrimeStatistics@ons.gov.uk and we will endeavour to help.