Effective immediately, everyone is paid hourly. If your employment contract doesn't specify your working hours, you work a 37½ hour week. Work in excess of your normal working hours may be paid at a higher hourly rate than your normal rate, but may not be paid at a lower rate. Falsifying your timesheet in either direction is a serious criminal offence. Employers must post the working hours claimed by their staff for public inspection, and workers are encouraged to shop their colleagues who are working more hours than they are claiming. Employers may not refuse to pay for hours worked even if it was in contravention of a direct order, but it may be treated as gross misconduct so you can sack them after you've paid them.
I think that the US actually has legislation to this effect for some classes of workers, but it's sadly unknown in the UK.
I'm prepared to make an exception for anyone who owns at least 5% of the equity of their employer.