I don't believe it's true, it certainly isn't something London could bring in on its own. However, gas appliances over here for apartments do need to have flame

I don't believe it's true, it certainly isn't something London could bring in on its own. However, gas appliances over here for apartments do need to have flame sensors (so the gas gets cut off), and if you're a landlord, you're going to need to do annual safety checks on gas equipment (apartment or not). So the equipment itself is slightly more costly for an apartment, and a landlord specifically has a strong incentive to have little/no gas, to save on the annual checks.