The amount of material, detected by routine screening, was extremely small and has been assessed by experts as posing no threat to the public, police say.

Heathrow had last month said it was unlikely to return to pre-pandemic demand for several years except at peak times.

Heathrow says it is working with airlines to agree on a mechanism that, if needed, would align supply and demand on peak days in the lead up to Christmas.

It says the decision has stabilised its operations, but it is still struggling with a lack of ground handlers.

This is part of efforts to limit traveller disruption as it struggles to cope with a rebound in demand.

Heathrow says that inbound leisure and business travel had remained weak however due to high levels of coronavirus in the country, and testing requirements for travellers leaving the country.

Heathrow also recorded a pretax loss of 1.79 billion pounds for 2021, taking total loses during the pandemic to 3.8 billion pounds due to the drop in passengers and high fixed costs.