If that's the Electrical Safety Standards in the Private Rented Sector (England) Regulations then they have been in force for a couple of years: https://www.nrla.org.uk/resources/looking-after-your-property/electrical-safety-inspections. As a landlord yourself didn't you already know that?
I think you've been misinformed a bit though. Those regs only cover private rentals, so about 4.8 million. I've seen ads around here for people to do the work and issue a certificate for £80, so your mate may have been overcharged. There isn't a requirement to repeat the test on change of tenant as far as I can see, just to give the new tenant a copy of the certificate.