Answer
An individual is entitled to exercise their rights to obtain information that is held about themselves under Data Protection legislation. This process is known as a subject access request. This is not a Disclosure Certificate.
A subject access request is an individual's right of access to verify the information held about them on police computers. A subject access request, to the Police National Computer, for instance, will either provide a letter stating that there is currently no information that the Chief Constable is obliged to disclose, or it will provide a list of all information held on the computer, including all convictions regardless of whether they are spent or not, and fixed penalty notices for disorder.
By law, subject access checks have to be done within 1 month of the request being received. There is no charge for this service. Although the police will consider every request, they are under no obligation to provide all of the data and there are exceptions to providing data e.g. if it is likely to jeopardise an investigation. A Subject Access Form is available to download from any Police website or from any police office. You should apply to the force area where you currently live or last lived in the UK. In order to complete the form, you need to provide two forms of identification, one with your name (a passport or driving licence) and the other with your current address (a recent utility bill or bank statement) and a cheque or postal order for the appropriate sum.
Subject access is not an appropriate process when going for a job or college course, this should be done through Disclosure Scotland, see SQ624.
In fact, if an employer insists you do a subject access check and show him/her the results, before giving you a job, s/he commits an offence under Data Protection legislation.