Jonathan Cloake, 37, who was operating the crane at a Barratt Homes development, died along with Michael Alexa, who was fixing his car next to the building site in Battersea in 2006.
Westminster Coroner’s Court heard the Falcon Cranes-owned machine should have had eight tons of concrete balancing the weight of its load but a manual was used for a different model which needed 12 tons.
The London Evening Standard reported that Health and Safety Executive inspector Brent Bolton said the extra weights would have increased the tension on a crucial set of bolts by ‘100-plus per cent’.
The 24 bolts on the crane’s slew ring had been replaced two months earlier after several suddenly broke while in use at the site.
Bolton told the hearing: “When we showed the manual that Falcon were using to the manufacturer, they told us that certain pages within the manual had been mixed up with those of other models of crane, and certain pages were missing.
“On every site that the crane was erected in the UK, it had an excess counterweight load on it – by between 16 per cent and 52 per cent.
“An overload of 52 per cent actually puts more than twice the force through the bolts on the slew ring, so the force being felt by the bolts increases by 100-plus per cent.”