A major incident was declared at the Marks & Spencer store in Charlton, southeast London, on Tuesday morning after carbon monoxide was detected throughout the building, prompting a large-scale emergency response.

The London Ambulance Service (LAS) confirmed it treated around 30 people for chemical inhalation, with 11 staff members taken to hospital for further assessment. It is understood that those affected were members of staff, as the store had not yet opened to the public at the time of the incident. No customers were involved.

According to Greenwich councillor David Gardner, six of the staff taken to hospital are undergoing further tests, with no injuries believed to be life-threatening.

The London Fire Brigade (LFB) was alerted shortly before 9am after carbon monoxide alarms activated within the store. Firefighters wearing breathing apparatus carried out a systematic sweep of the building using specialist detection equipment and confirmed elevated carbon monoxide readings throughout the premises.

Crews subsequently ventilated the building and completed further checks to ensure levels had reduced. Around 35 people evacuated the building before emergency services arrived, with firefighters assisting ambulance crews in treating those affected at the scene.

The emergency response included two fire engines, two fire rescue units, conventional ambulance resources, and specialist teams including the Hazardous Area Response Team (HART).

James Johnson, Strategic Commander for the London Ambulance Service, said crews were deployed alongside advanced paramedic practitioners to manage the incident safely and assess those exposed.

An M&S spokesperson confirmed the Charlton store has been temporarily closed while investigations continue, adding that the company hopes to reopen the store once safety checks are completed.

The cause of the carbon monoxide presence has not yet been confirmed.

Incidents of this nature underline the critical importance of robust gas safety management on construction and refurbishment projects. In live buildings, particularly during refurbishment works, gas services may remain operational even where their status is unclear or undocumented. 

All services should therefore be treated as live unless positively isolated, tested, and confirmed otherwise. Inadequate identification, isolation or monitoring of gas systems can lead to undetected leaks, with carbon monoxide presenting a serious and often invisible risk to occupants and workers alike. Effective planning, clear service records, competent isolation procedures and continuous monitoring are essential to preventing similar incidents in both occupied buildings and active construction environments.