Professor Helen Young, The Chief Nurse and Executive Director of Patient Care at the South Central Ambulance Service NHS Foundation Trust (SCAS) 

At 11:30 on 25 June, South Central Ambulance Service declared a critical incident. The trust cited extreme heat and a sharp rise in Category 2 response times, and said openly that those times were longer than they should be. Just over 32 hours later, at 8pm on 26 June, it escalated to a major incident, allowing it to request national mutual aid and bring in crews from Yorkshire. Somewhere in the hours between those two declarations were patients whose ambulances arrived late, and in some cases too late for anything to be done.

Board papers this week show that the trust has issued duty of candour letters in 39 cases arising from the heatwave. Twenty-one are recorded as deaths. The chief nurse, Professor Helen Young, has said it has not yet been established that delays contributed to each death, and clinical reviews continue. Her role places her at the centre of the trust's patient-safety response: as Chief Nurse and Executive Director of Patient Care, she is responsible for clinical governance, quality standards and advising the board on patient safety. The distinction she has drawn is essential. A recorded death is not proof of causation, and the investigations must establish what part, if any, delayed ambulance care played in each case. Writing to families and reporting the figures to a public board are, meanwhile, part of the duty of candour regime working as it was designed to.

The wider lesson concerns what the NHS has chosen to measure. The Medium Term Planning Framework asks ambulance services to bring the average Category 2 response, which covers suspected heart attacks and strokes, down to 25 minutes in 2026/27, with the 18-minute standard restored by 2028/29. Annual averages reward efficiency in ordinary conditions. They say little about how a system behaves when heat and demand rise together, and a target that is met in April and abandoned in a heatwave describes the April system. A trust can be improving on paper and still have no margin on the days that matter most.

Heat is among the most forecastable hazards the service faces. Warnings were in force before the pressure peaked, and the neighbouring South East Coast Ambulance Service also recorded unprecedented numbers of life-threatening calls on 25, 26 and 27 June. This was a regional shock, so it cannot be put down to one trust's misjudgement. Even so, the formal response began with declarations made once response times had already slipped. Escalation that follows the queue is escalation that arrives late.

The government's health plan leans heavily on shared data platforms and digital dispatch. That raises a question every board should now be able to answer: how does each critical system behave when ambient temperatures exceed those for which it was designed? The answer should be documented, tested and reported to directors before the next warning. Capital rules in the NHS seldom reward cooling, redundancy or spare vehicles, and deferred investment tends to resurface later as an incident report.

Workforce sits underneath all of it. Executives have acknowledged that frontline staff worked under extraordinary pressure, and the trust has warned that relying on individual goodwill in a crisis is unsustainable. That is a candid sentence for an NHS board to publish and should be read as a finding. Operational staff were stood down from non-essential duties and redeployed to frontline shifts. Crews were asked for extra shifts and overtime, and colleagues travelled from another region to cover the north of the patch. These measures can be used once or twice a summer. They are not a plan, and staff who absorb the strain without recognition in the planning model are the ones who eventually leave.

The practical questions are narrow and answerable. Trust boards need escalation triggers tied to extreme heat warnings, so that surge arrangements begin before the queue does. NHS England and commissioners should ask whether a performance regime built on tight averages leaves trusts any slack to hold in reserve. Suppliers of dispatch and records software should expect resilience evidence to become a procurement requirement, with consequences attached. Public trust will depend on how openly the findings are published. A family told that delay may have contributed to a death will want to know what has changed before the next warning is issued.

The trust's investigations will take months, and the next heatwave will not wait for them. Whether the NHS enters next summer with the same dependencies and the same targets is being decided now, in the winter planning round.