Apollo Property Services – now part of Keepmoat Group – was sentenced following the incident at the Abbey Road Estate, on Adelaide Road, Camden, between 18 February and 18 March 2008.

The Old Bailey heard during a two-week trial that seven residents were exposed to CO because boiler flues servicing the flats were obstructed during roof refurbishment work.

An HSE investigation found that Apollo knew that some flues may still be serving boilers in the properties, but did not have an adequate system for inspecting them. So work continued without checks being carried out.

The company also failed to ensure that the work was adequately supervised, and did not ensure that workers were familiar with safe working practices in relation to gas flues or were aware of the risks.

Apollo Property Services Group Ltd was fined £165,000, ordered to pay £117,582 in costs and a total of £19,000 in compensation after being found guilty of safety breaches.

After sentencing, HSE’s Inspector Helen Donnelly said: “Despite the client’s adviser warning the company to consider the risk of blocking or covering flues at the start of the refurbishment project, the company did not assess the risks to residents or have a safe system to ensure flues serving live boilers were not obstructed.

“Moreover, as part of one of the UK’s largest property service organisations, Apollo Property Services Group Limited is very experienced in refurbishing housing estates so there is no reason for this incident to have happened.”

Tony Leach, Health & Safety Director for Apollo, said: “We fully accept the decision and would like to take this opportunity to once again apologise unreservedly to the families affected by this incident.

“Safety is our number one priority and we have carried out a full review of our procedures and training to ensure that all staff, and subcontractors, working on our schemes meet the high standards we expect.”