One of the UK's largest property service organisations has been ordered to pay more than £300,000 in fines, costs and compensation after seven people were hospitalised when carbon monoxide (CO) fumes escaped into their homes.

Apollo Property Services Group Ltd, now part of Keepmoat Group, was sentenced on 17 December in relation to the incident at the Abbey Road Estate in Camden, between February and March 2008.

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

An investigation by the Health and Safety Executive (HSE) found that Apollo knew 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 was fined £165,000, ordered to pay £117,582 in costs and a total of £19,000 in compensation after being found guilty of breaching section 3(1) of the Health and Safety etc. at Work Act 1974.

HSE 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.