The child's imitation weapon was left in a bag on a flight from Paris, from were the dignitaries had boarded through a VIP channel.

Civilian security guards in London alerted police after discovering the forgotten luggage on Monday evening. But the toy was returned to its owner once its innocent nature had been established, Scotland Yard said.

A Yard spokesman said: "Police officers attended and worked out it was a toy gun. It was returned to the owner."

The royal members boarded the flight from Charles de Gaulle Airport, but it is not known how the toy gun passed through security in Paris.

The bag was found in the cabin of the flight once the passengers had disembarked at Heathrow. After finding what looked to be a gun, guards called for police assistance.

The situation was resolved, with the toy handed back to its owner. But the incident could lead to red faces among security staff in Paris for allowing the toy gun on to the flight.