Britain is heading into a period of extreme heat, with the Met Office issuing warnings of temperatures approaching 40°C, and the question arriving in every HR inbox and group chat is identical: at what temperature does work legally have to stop? The honest answer is uncomfortable for everyone involved. There is no number.

UK law sets no statutory maximum workplace temperature. The Workplace (Health, Safety and Welfare) Regulations 1992 require only that indoor temperatures be reasonable, a word carrying extraordinary weight when the thermometer reads 38°C. As the current heatwave deepens, UK business groups have publicly rejected calls to introduce a legal maximum, leaving workers and HR teams to negotiate heat safety in real time, without a regulatory floor to stand on.

What the law actually says (and what it doesn't)

The Health and Safety Executive (HSE) is explicit that no statutory minimum or maximum temperature is fixed in law. Employers carry a general duty under the Health and Safety at Work Act 1974 to protect workers from foreseeable harm, and the Workplace (Health, Safety and Welfare) Regulations 1992 specify only that indoor temperatures should be reasonable. His Majesty's Revenue and Customs (HMRC) tax treatment of employer welfare spend is a separate matter; the operative framework here sits with the HSE and the Employment Rights Act 1996.

The Advisory, Conciliation and Arbitration Service (ACAS) reinforces the same point in its published guidance: employers are expected to assess thermal risk and take appropriate action, but no specific temperature cut-off triggers a mandatory intervention. What this produces in practice is a duty that is real but deliberately flexible, shaped by the type of work, the building, the workers involved, and the adequacy of the employer's documented response.

The Trades Union Congress (TUC) and UNISON have called for a legal indoor maximum of 30°C, or 27°C for physically strenuous work, with active mitigation measures triggered above 24°C. The British Safety Council and independent climate advisers to the UK government have also pressed for a statutory limit, pointing out that temperatures above 40°C are forecast to occur with growing frequency across England and Wales. Business groups have resisted, arguing that a fixed ceiling would be too blunt to accommodate the genuine diversity of UK workplaces, from chilled logistics hubs to school kitchens to open-plan offices in Victorian buildings.

For employees: what you can actually do

The absence of a legal number does not mean you have no recourse. It means your recourse runs through the reasonableness standard, your employer's duty of care under the 1974 Act, and your right under statute to refuse work you genuinely believe is unsafe. The following steps hold up under the existing framework.

• Document the conditions. Note the indoor temperature, the time, the task being performed, and any physical symptoms such as dizziness, headache, or nausea. A photograph of a thermometer reading in your workspace is a legitimate contemporaneous record.
• Raise it formally in writing. Email your line manager or HR team. Reference your employer's duty under the Health and Safety at Work Act 1974 and ask what thermal risk assessment has been carried out for the heatwave period. A written request changes the evidential position for both sides.
• Ask about practical adjustments. Flexible hours to avoid the hottest part of the working day, a relaxed dress code, additional water and rest breaks, fans, window coverings, and where the role permits it, remote working arrangements. These are reasonable requests, not requests for special treatment.
• Know your refusal rights. Under section 44 of the Employment Rights Act 1996, you cannot lawfully be subjected to a detriment for leaving, or for refusing to attend, a workplace you reasonably believe presents a serious and imminent danger to your health. This is a deliberately high bar rather than a general discomfort threshold, but it is a real statutory protection and it is worth knowing it exists.
• Escalate if the response is inadequate. If your employer dismisses the risk without documented justification, you can contact your trade union, raise a concern directly with the HSE, or seek guidance from ACAS. Outdoor workers, warehouse staff, construction crews, and anyone working in a building without mechanical cooling carry particularly strong grounds to request documented risk mitigation.

For HR: your obligations don't pause because the number is missing

For those managing people operations through a heatwave, the absence of a statutory temperature ceiling is not a defensible position in itself. It is, if anything, a risk multiplier. The general duty of care under the Health and Safety at Work Act 1974 applies at every temperature; the difference at 38°C is that the consequences of an inadequate risk assessment include heat-related illness, significant productivity losses, and exposure to Employment Tribunal claims under section 44 or section 100 of the Employment Rights Act 1996.

The Chartered Institute of Personnel and Development (CIPD), which represents around 160,000 HR and people professionals in the UK, has consistently noted that documented thermal risk management sits within the broader wellbeing obligations HR teams carry. A defensible heat response involves the following in practical terms.

• Run and document a heatwave risk assessment. Cover indoor temperature readings, ventilation adequacy, task intensity, personal protective equipment constraints, and the needs of vulnerable workers, including those who are pregnant, older, taking relevant medication, or managing underlying health conditions. The documentation is the evidence that the reasonableness standard was actively applied rather than assumed.
• Publish the plan before workers ask. A short communication from HR setting out adjusted hours, hydration arrangements, dress code relaxation, remote-work eligibility, and the route for raising a concern does more for workforce trust than any reactive response to a formal grievance.
• Brief line managers on the refusal pathway. Section 44 detriment claims frequently arise because a frontline manager treated a heat refusal as insubordination rather than a statutory right. A short briefing covering the legal position and the required response prevents the majority of these situations.
• Account for the productivity cost. Research examining UK heat-related productivity losses places the figure in the billions of pounds across a significant heatwave period. Reasonable adjustments are not a goodwill gesture; they are a straightforward loss-mitigation measure.
• Treat this as standing policy, not a seasonal reaction. The independent advice provided to the UK government on climate adaptation is consistent: extreme heat events above 40°C will recur and will intensify. A standing heat policy, reviewed each spring and stress-tested against the ACAS guidance, is considerably cheaper to build now than to defend under tribunal scrutiny after the fact.

The bigger question: why no number?

Business groups argue that a fixed legal maximum would be too rigid for a country whose workplaces range from steel-processing facilities to chilled food warehouses to open-air construction sites. Unions, particularly the TUC and UNISON, argue the opposite: that the reasonableness standard, written in 1992 for a measurably cooler climate, has become functionally unworkable, and that a clear statutory cap (30°C indoors, 27°C for strenuous work) would give both workers and employers a defensible shared reference point.

The Workplace (Health, Safety and Welfare) Regulations 1992 derive in part from the framework established by European directives that were in force at the time of UK accession. Post-2020, the UK can amend these Regulations independently without reference to EU processes, which means a statutory maximum temperature is now entirely a domestic political choice rather than a matter of Brussels consultation. The TUC and the British Safety Council have made this point directly: the legislative path is clear; the obstacle is political will rather than constitutional complexity.

For job-seekers reading this during an extreme-heat week, there is a practical signal worth noting. How a prospective employer talks about heat, ventilation, flexible hours, and remote-work eligibility is a genuine indicator of workplace culture. Asking a hiring manager about the organisation's heatwave policy belongs in the interview conversation now, alongside questions about salary and progression. Verified reviews from current and former employees, of the kind published on workforce intelligence platforms, frequently surface the gap between a company's stated wellbeing policy and the daily reality for the people working inside it.

What to watch next

Three developments are worth tracking through the remainder of this summer and into the next legislative cycle. First, whether the political pressure generated by a sustained 40°C event is sufficient to prompt a government consultation on a statutory temperature limit, or whether organised business resistance continues to hold. Second, whether Employment Tribunal cases involving heat-related detriment, constructive dismissal, or section 44 refusal claims begin to accumulate at a rate that generates the kind of slow case-law shift that has historically preceded regulatory action in other areas of UK health and safety law. Third, whether sector-level collective agreements, particularly in construction, logistics, and food production, begin incorporating heat clauses ahead of any statutory change, effectively creating a patchwork floor that mirrors the outcome unions are seeking at the legislative level.

Until any of that resolves, the practical floor is the one workers and HR teams construct together, assessment by assessment, written record by written record. The HSE's guidance is real, the ACAS advice is available, and the statutory protections under the Employment Rights Act 1996 exist right now. The legal number does not yet exist. The duty of care does.