its twice a year not daily.
naturally your body clock would change with the light anyway, its unnatural to wake up at an arbitrary fixed time, rather than say sunrise.
Yeah but it's twice a year for the entire country, over a large population that can mean big costs to the NHS. There's loads of sleep studies and how it affects people. It can affect cortisol, blood pressure, food cravings, etc - so when you do all those little things to 65 million people twice a year it's going to cause damage to some people, probably those who were already vulnerable in the first place. Imagine a shift worker who was already struggling with sleep now has to get up an extra hour early, it adds up.