The initial findings of an HSE investigation into the tragedy have been confirmed in a letter from minister Mike Penning to the International Powered Access Federation.

Operator Rick Jaeger-Fozard was killed when the Genie Z-135/70 collapsed at the Kimberly Access yard next to the motorway near Heathrow.

Penning said: “HSE’s Health and Safety Laboratory began their examination of the Mobile Elevating Work Platform on 17 July 2013 in the presence of a representative of its manufacturer.

“Their initial findings were that it appeared that the machine in question may not have been calibrated correctly.

“This may have allowed the basket to be extended to a position in which the MEWP became unstable.”

The HSL is now carrying out a detailed technical examination of the control system to substantiate these findings.

The IPAF trade body wrote to the Government last month to express its concerns about the lack of any interim findings following the tragedy.

Around 200 similar machines are used on sites around the country.

Penning said: “No safety alert has been issued on this occasion for the reasons explained above, the HSE has no evidence at present which would suggest that these machines are unsafe when properly calibrated and used.”

IPAF CEO Tim Whiteman said: “We appreciate the Minister’s response and will consult with our members and the IPAF UK Country Council on the next steps.

“MEWP safety is IPAF’s top priority and will remain so.”