There have been precisely zero new reservoirs brought into service in England over the last 30 years while the population has as you say grown considerably. There has been relatively little infrastructure maintenance, leading to high-levels of leakage, and over-extraction from once healthy rivers. I'd agree that things weren't perfect in 1976 but privatization has failed to noticeably improve things either while totally failing to prepare for the changes required by a growing population and worsening climate.
Water leakage is not a problem. The water goes back into the aquifer, where it should be anyway. It's a minor waste of energy and treatment chemicals, since it's drinkable water, but the water itself is not lost.
