Under the Regulatory and Investigatory Powers Act 2000 (RIPA) some public authorities (e.g. the police) are empowered to ask a college or university to produce or disclose to them certain communications data for specified purposes e.g., for prevention of crime.
The Kent Police website contains a useful publication on this titled Accessing Communications Data accessible at http://www.kent.police.uk/
The relevant part of this policy guidance notes RIPA - Part 1, Chapter 2 provides a legislative regime for Public authorities, e.g. Law Enforcement, to access (obtain) the communications data of persons, in compliance with the Human Rights Act 1998 and the European Convention of Human Rights. Mechanisms used under this part of RIPA to obtain legal authority to acquire data mirror that under other parts of RIPA.
Further, communications data can only be accessed lawfully for one of the following purposes under the Regulation of Investigatory Powers Act 2000.
1. in the interests of National Security S22 (2) (a)
2. for the prevention and detection of crime or preventing disorder S22 (2) (b)
3. in the interests of the economic well being of the United Kingdom S22 (2) (c)
4. in the interests of public safety S22 (2) (d)
5. for the purpose of protecting public health S22 (2) (e).
Materials relating to acts of terrorism will most likely fall under one or all of these sections. However, the university should exercise discretion and should go about accessing the data only upon clear guidance being from the police. The Association of Police Officers (ACPO) has published a good a practice guide (though focussed principally at police officers and other law enforcement authorities) which deals with the procedures to be used in the recovery of computer based electronic evidence. The guidance can be accessed at http://www.7safe.com/electronic_evidence/ACPO_guidelines_computer_evidence.pdf
We can conclude that the legal position is thus that upon a request being made by the police, files from the employees PC might need to be extracted to comply with the law.