Simple answer? No, it’s not a legal requirement. We strongly advise it though. The amount of people annually who receive shocks, burns, and injury from faulty electrics is in the hundreds of thousands.
Testing your property to ensure that the wiring, installations, and appliances are safe seems a small expense when you consider what’s at risk. If the unthinkable happens and your tenant receives an injury, a PIR or PAT test certificate are the only things you can produce to show that you’ve taken all possible steps to prevent such an incidence.