The sites visited involve roof work, extensions to domestic properties, and general refurbishment.
HSE figures show there have been 59 fatalities in London between 2004/2005 and 2009/2010, 30 being deaths from falls. Over 70% of the deaths caused by a fall occurred on small sites.
Over the next few weeks inspectors will visit sites in Brent, Westminster, Kensington & Chelsea, Newham, Redbridge, Camden, Enfield, Haringey, Lewisham, Bromley, Richmond and Wandsworth.
Inspectors will concentrate on how sites are managing roof repair, working at height and manual handling, as well as the welfare facilities for workers. Inspectors prefer to offer advice but will take enforcement action to stop unsafe work and ensure any essential improvements are made.
Andrew Beal, HSE principal inspector, said: "Each year too many construction workers are needlessly injured or killed while working on site. Finding such poor work practices that we had to issues prohibition notices on nearly one in four sites is unacceptable, especially when many of the incidents are completely avoidable by taking commonsense actions and precautions."