Whilst PAT testing is not strictly compulsory, it is generally regarded as being the best way of meeting the electrical regulations that exist to protect employees, customers and tenants. Without it you could be in a very difficult situation if an electrical accident were to occur.
All portable electrical equipment is subject to getting damaged during use, and this damage could render the equipment dangerous to the user. Without a regular programme of testing and inspection, you have not taken reasonable steps to ensure the safety of users.
Tests and inspections should be made at reasonable and regular intervals, bearing in mind the rate of use of both portable and fixed appliances.
Failure to comply with the Electrical Regulations may constitute a criminal offence under the Consumer Protection Act 1987 which carries a maximum penalty on summary conviction of a £5,000 fine and/or 6 months imprisonment. Landlords and letting agents could also be sued in Civil Law under the duty of care for failure to ensure the tenants safety and and, as a result, face punitive damages.