Employee records should be kept for the statutory period which depends on the type of information that is kept. Data privacy laws, for example the Data Protection Act 1998 and more recently GDPR stipulate the retention and privacy protection that certain data are afforded. For the most part these range from 3 years to 6 years and in some cases up to 10 years. It all depends on the type, and there are some extremes such as up to 40 years for some types of accidents, for example, think about after effects of asbestos exposure for employees from the 1980s and 1990s, that should provide some perspective.
The best resources for understating HR record keeping is in fact the government website. There are also websites such as the CIPD, which are invaluable sources of information for the HR professional as well as company owners and managers.
The type of data determines the statutory retention period
The CIPID has a great fact sheet that tells you which retention period applies and the law from which the retention period is derived.