It's a bit more than a couple of quid. It's a tenner. You have to submit a written request and submit proof of your identity, together with the fee. The police have to send you details of what they've got on file within 40 days.
The easiest way to submit your request is to use the form which most police forces have on their websites. To find the form, Google this line:
xxxxxxxx police subject access
replacing xxxxxxxx with the name of your county (e.g. Suffolk) or the name of your local police force (e.g. Metropolitan).
Chris