Have a look at the Right Care Atlas of Variation  in Diagnostic Services. http://www.rightcare.nhs.uk/index.php/atlas/diagnostics-the-nhs-atlas-of-variation-in-diagnostics-services/

‘Diagnostic services are of great importance in the NHS because, when used correctly, they support or rule out potential diagnoses, and underpin the effective and efficient management of patient pathways.

Unwarranted variation in the rates of diagnostic testing is of the utmost relevance to individual patients with the over-use, as well as under-use, of diagnostic tests being potentially serious issues. For example, effective capacity planning in imaging services should enable improved patient access balanced against the need to avoid over-use of interventions that have the potential to cause harm, such as ionising radiation…’

If you use the interactive online version you can see data for investigations per 100,000 population across different organisations.