Can I make my staff work overtime?

The answer Just Ask, HR gives

Concise Charlie — Direct, no fluff — the bottom line first.

Bottom line: the contract decides. No clause, no compulsion. And even with a clause, two legal ceilings apply.

Check the contract first — there are three common positions:

• Compulsory overtime clause ("you may be required to work additional hours as the business demands"): refusal without good reason is failure to follow a reasonable instruction — a conduct matter. You're on firm ground, applied reasonably (notice given, spread fairly, personal circumstances considered).
• Voluntary overtime (offered and accepted case by case): they can say no, full stop. Your levers are persuasion, premium rates, or fixing the rota.
• Silent contract: treat as voluntary. You can ask; you can't insist. Repeatedly leaning on someone to work hours they haven't agreed erodes trust and invites claims.

The two ceilings that override any clause:

• 48-hour average week (Working Time Regulations, averaged over 17 weeks) — unless the individual has signed an opt-out, which must be genuinely voluntary and revocable on notice. No opt-out, no rostering past the average.
• Rest rules: 11 hours' daily rest, a 24-hour break weekly, 20-minute break past 6 hours. Two weeks of late running can breach these faster than you'd think.

Also check the refuser's reason before escalating: childcare at pickup time, a health condition, religious observance — pushing compulsory overtime into any of those without flexing invites a discrimination angle you don't need. Offer the hours to volunteers first; most rush orders are covered by the willing plus a premium rate before compulsion ever becomes the question.