The UK Health and Safety Executive along with insurance companies will expect you to perform PAT testing to ensure that you are compliant with certain regulations including:
Health and Safety at Work Act of 1974
The Electricity at Work Regulations of 1989
The Provision and Use of Work Equipment Regulations of 1998
The Management of Health and Safety at Work Regulations of 1999
Not complying with the above mentioned regulations can result in fines up to £5,000 and/or six months imprisonment. Fines have been seen to go as high as £20,000 and offences heard in the Crown Court have carried sentences of more than 2 years imprisonment in additional to unlimited financial penalties. So even though PAT testing itself is not legally required, it simply helps you to protect yourself by ensuring that you are complying with these regulations.