From Wiki

The system for getting police checks from the UK is in transition - police checks issued after December 31st 2008 should be the new-style ACPO checks.

[Current police check instructions for UK applicants].

Note: The above link is only for Immigration Purpose. If you are asked to obtain a Police Check for Employment Purposes (such as Enhanced Reliability) then you need to approach Disclosure Scotland (www.DisclosureScotland.com).