Is PAT testing a legal requirement?

The Electricity at Work Regulations state in Regulation 4(2) that:
As may be necessary to prevent danger, all systems shall be maintained so as to prevent, so far as is reasonably practicable, such danger.
This regulation concerns the need for maintenance to be done as a precautionary measure to ensure safety of the system if danger would otherwise result. Maintenance should be performed on a regular basis in order to be sufficient to forestall any dangerous situations from occurring so far as is reasonably practicable.
The equipment should be examined regularly and electrical testing should be carried out for the purposes of preventive care. Real-world experience on the use of equipment and conditions prevailing can indicate a change to the frequency at which preventive maintenance needs to be done. This is an issue for the responsible person to judge. They need to locate all data needed to make the right judgment on pat testing, including referring to the manufacturers guidelines.