Answer depends on what kind of company, but still is likely to be unclear...

Rules need to be spelled out
http://wapurl.co.uk/?NMQL525
"The Data Protection Act DPA says that data should be kept for as long as is necessary for the purpose it was obtained," explained James Mullock, a lawyer with law firm Osborne Clarke. And you can't get much more vague than that."

Systems to resolve the e-mail crunch
http://www.tmcnet.com/usubmit/2007/09/03/2906686.htm
"There are a number of UK regulations that enforce the retention of e-mail.

The Freedom of Information Act dictates that public sector bodies must be able to supply copies of "recorded information" on request, even if generated before the act came into force in 2005.

Through the Data Protection Act, a member of the public can request information held about them.

And there are also industry-specific controls, such as those enforced by the Financial Services Authority, which require all e-mails be held for six years.

In addition, there are the increasingly onerous evidential requirements of court proceedings, which require a verifiable e-mail audit trail from "reliable" systems to be admissible."