It came about because gas installations in rented properties were killing far more people than those in owner-occupier properties.
And what makes you think anyone tested anything when the conversions to natural gas were done? I remember them giving up trying to convert my father's Ideal Standard boiler, and they just left it in bits on the kitchen floor. My father did the conversion when he got home in the evening, but we never saw or heard from the the gas board contractors again, so as far as they know, it's still in bits on the kitchen floor.
I wonder how long before we convert back to town gas?