On-Site On-Call vs. Off-Site Standby – The Distinction That Matters

The distinction between on-site on-call duty (where presence at a designated location is required) and off-site standby (where the worker remains contactable from a location of their choice) determines whether an entire night counts towards statutory maximum working hours or not at all. It is one of the most consequential distinctions in UK working time law under the Working Time Regulations 1998 (WTR 1998) and retained EU case law (Directive 2003/88/EC).

Three Forms of Availability

On-Site On-Call Duty: Full Inclusion in Working Time

In the landmark Jaeger ruling (C-151/02), the European Court of Justice (ECJ) established that on-call duty requiring personal presence at the workplace constitutes working time in its entirety — regardless of how much active work is actually carried out during the shift. UK statutory employment law adheres strictly to this standard for health and safety purposes under the Working Time Regulations 1998.

Practical consequence: A 24-hour shift inherently breaches the 48-hour average weekly working limit or daily rest entitlements unless a valid individual opt-out agreement under Regulation 5 WTR 1998, a relevant workforce agreement, or specific statutory derogations (such as Regulation 21 WTR 1998) apply with appropriate compensatory rest.

Off-Site Standby: Relative Freedom and Crucial Limitations

Off-site standby may, in principle, coincide with a worker’s daily rest period. However, established case law concerning standby and on-call arrangements (including Matzak C-518/15 and DJ v Radiotelevizija Slovenija C-344/19) has refined this principle: The decisive criterion is whether the constraints and obligations imposed by the employer significantly impair the worker's ability to freely manage their personal leisure time.

Criteria for overall legal assessment:

• Response and arrival time. The shorter the required response window, the more likely the period is classified as full working time. An arrival window of just a few minutes strongly indicates working time.
• Frequency of call-outs. Frequent call-outs during the shift weigh heavily in favour of full working time classification.
• Additional constraints. Mandatory wearing of a uniform, an obligation to use a company vehicle, or strict geographic limitations confining the worker to an excessively narrow radius.

Impact on Mandatory Daily Rest Periods

An active call-out during off-site standby breaks the continuity of the 11-hour uninterrupted daily rest period required under Regulation 10 of the Working Time Regulations 1998, so the eleven consecutive hours run from the point the call-out ends:

For example, after an emergency call-out lasting 30 minutes at 3:00 AM, an employer cannot show that the Regulation 10 entitlement was afforded if the employee is rostered back onto their standard shift at 7:00 AM, unless a statutory derogation applies. Under Regulation 21 and Regulation 24 WTR 1998 (applicable to sectors such as healthcare, residential care, utilities, and emergency services), where daily rest cannot be taken, the employer is legally obligated to provide an equivalent period of uninterrupted compensatory rest.

Remuneration and the National Minimum Wage

Occupational health and safety rules (working time limits under WTR 1998) and remuneration provisions under the National Minimum Wage Act 1998 (NMWA) are legally distinct concepts:

• Health and safety: All on-call hours at an employer-designated location count 100% towards working time limits.
• Remuneration and Minimum Wage: Following the Supreme Court ruling in Royal Mencap Society v Tomlinson-Blake [2021] UKSC 8, workers performing sleep-in shifts who are expected to sleep and only provided with sleeping facilities are only entitled to the National Minimum Wage / National Living Wage for the time they are awake and carrying out active duties, unless their employment contract provides for a higher or flat hourly rate.
• Standby remuneration: For off-site standby, an availability retainer or standby allowance is customary, while actual call-outs must be remunerated at the agreed contractual rate plus any applicable overtime, night, or weekend enhancements.

Crucially, an employer must ensure that total remuneration in any pay reference period divided by total qualifying hours worked never falls below the statutory National Living Wage rate. Complete payroll and time records must be retained for at least 6 years under HMRC and NMWA compliance rules.

Requirements for Working Time Recording

To remain compliant with statutory regulations, ECJ case law (CCOO C-55/18), and Regulation 9 of the Working Time Regulations 1998, employers must maintain adequate, accessible, and reliable records. Time tracking software must support distinct categories:

1. On-Site On-Call Duty — Recorded fully as working time for maximum hours and rest tracking, with differentiated contractual pay rates.
2. Off-Site Standby — Recorded as non-working availability time, compensated via agreed standby allowances.
3. Active Call-Out During Off-Site Standby — Recorded down to the exact minute, counting towards working hours, triggering applicable enhanced rates, and factoring into compensatory rest tracking.

The third category is essential. Without minute-accurate recording of active interventions, employers cannot substantiate compliant rest periods or defend against claims before an Employment Tribunal or enforcement action by HMRC.

Sources and Statutory Foundations

Statutes and Directives

• Working Time Regulations 1998 (SI 1998/1833), Reg 2 / Directive 2003/88/EC (Art. 2) — Statutory definition of working time and rest periods.
• Working Time Regulations 1998, Reg 10 & 24 — Uninterrupted daily rest period of 11 hours and compensatory rest requirements.
• National Minimum Wage Act 1998 & National Minimum Wage Regulations 2015 — Pay reference periods and calculation of minimum wage hours.
• Employment Rights Act 1996 — Written statement of particulars, deductions from wages, and statutory protections.

Case Law

• Supreme Court, Judgment of 19 March 2021 – Royal Mencap Society v Tomlinson-Blake [2021] UKSC 8 — National Minimum Wage entitlement for sleep-in workers limited to periods of active wakefulness.
• ECJ, Judgment of 9 September 2003 – C-151/02 (Jaeger) — Standby duty requiring physical presence at the workplace constitutes working time in its entirety.
• ECJ, Judgment of 21 February 2018 – C-518/15 (Matzak) — Standby time at home constitutes working time where mandatory response constraints severely restrict personal leisure.
• ECJ, Judgment of 9 March 2021 – C-344/19 & C-580/19 (DJ v Radiotelevizija Slovenija / RJ v Stadt Offenbach am Main) — On-call duty is classified as working time only when cumulative constraints significantly impair the free management of personal time.

Status of legal evaluation: August 2026. This article provides general guidance and does not constitute formal legal advice.