I've worked all weekend unpaid. Can I take a day off in return?

Many companies operate a Time Off In Lieu policy (often abbreviated to TOIL). This means that employees can claim back extra time that they have worked, by taking equivalent time off within a set period and arrangements.

If your employer operates such a scheme, you will be able to find details of it in your staff handbook. You have to remember that any TOIL scheme is a matter for your contract of employment, so if your scheme is not particularly generous, or your employer doesn't even offer one, you don't have a statutory legal right to the time off.

If your employer does not operate a TOIL scheme, it might be worth approaching your manager anyway, as they may still be able to offer you time off at their own discretion if you have been putting in extra work unpaid.

It may be the case though that your contract or staff handbook includes a clause which permits your employer to expect you to work extra days without being able to claim anything back. This might say something along the lines of "May occasionally be required to work weekends". Flexible working is a priority for trade unions, so if there's a union at your workplace, they are more likely to have negotiated a TOIL-type agreement, or appropriate pay or overtime to compensate for this.