Westminster Magistrates’ Court heard that four people were injured, three seriously, in the incident on 7 March 2012.

They included 25 year-old Charlotte Hammond, from Romford, who sustained an open fracture of her right ankle that required extensive surgery.

The 3.6 metre high hoarding had been put up the previous day by Wiltshire-based Oracle Interiors Ltd to fence off a clothing store that was being refurbished.

The shopfitting firm was prosecuted on Wednesday after an HSE investigation identified serious flaws with the temporary structure.

The court heard the hoarding was held in place by a single timber brace.

It was inherently weak and wasn’t designed or installed to sufficiently withstand gusts of wind or knocks from passing shoppers, both of which should have been factored in.

An estimated 20 people were trapped by the hoarding when it came down although most managed to escape unharmed as emergency crews and fellow passers-by rushed to help.

Injuries sustained by the other victims, none of whom want to be identified, included broken bones in the back and crushed nerves in an arm.

Oracle Interiors Ltd, of Salisbury, was fined £10,000 and ordered to pay £13,069 in costs after pleading guilty to a single breach of the CDM regulations.

After the hearing, HSE Inspector Wendy Garnett said: “The law clearly states that all temporary structures, including hoardings, are properly designed, and so installed to withstand any foreseeable loads imposed on it.

“That clearly wasn’t the case on this occasion and innocent shoppers were subjected to a frightening and, for some, hugely traumatic ordeal that had a long-term impact.

“Charlotte and others could easily have been killed by the hoarding and they were completely unaware that it posed a risk – not only to them, but to the tens of thousands of people who walked along Oxford Street that busy afternoon.

“Oracle Interiors Ltd could and should have done more to prevent the collapse.”