To the best of my knowledge previous employers are only allowed to release very basic information to a prospective employer.
I believe sickness, punctuality, performance and any disciplinary matters are not made public to the new employer. I was in the police service for 15 years and I was disciplined a couple of times for minor things in which I received management advice which went on my personnel file.
New Data Protection laws came in last year to replace the existing Data Protection Act that had been in since 1998. The new laws now cover the use of internet information which was in it's infancy twenty years.
These new laws are extremely strict and are tipped in favour of people and their personal information. For example, a company such as Tesco's who know about your shopping habits if you collect store points are now forbidden to pass on your information to outside marketing agencies unless you have given your expressed permission. I appreciate I may be going off subject here so I apologise.
Going back to the original topic, a period of sickness from work is technically sensitive information that contains details of why you were sick and it may also contain referrals that were made to occupational health that are again strictly confidential.
I would assume that a past employer such as the police would only release details of the dates of your service (when you joined and when you left), your rank (or job title) and perhaps how you left (retired, resigned or dismissed).
I hope this has been of some help!
