Police discovered a potentially explosive package today in one of the three sites being searched as part of an investigation into suspected organised crime gangs.

The suspicious package was found in a safe deposit box in Finchley Road between Childs Hill and West Hampstead as police searched thousands of safe deposit boxes across three sites, one of which is in Edgware.

The A41 was cordoned off between the Esso Garage at the junction with Hendon Way and Finchley Road and Frognal train station at around 3.15pm.

The closure caused gridlock leading up to the scene and at least 12 buses were taken out of service on the 113, 82 and 328 routes.

Armed police, the ambulance service, and crews from the London Fire Brigade also attended the scene. The A41 remained closed for about an hour this afternoon.

Hamid Zendehpir, 31, works in the Tehran Supermarket next to the Finchley Road site.

He was forced to get off an 82 bus and wait until the cordon was cleared before he could get to the shop.

"The last few days have been very frightening," said Mr Zendehpir.

"I have never seen this situation before with police and guns outside on the street.

"It has been busy with police, people are worried about what is going on and it has caused a lot of disruption in the area."

The investigation, which involved 300 police officers, was the first of this scale the Metropolitan Police has ever conducted against suspected criminals using safe boxes to store their assets.

Codenamed Operation Rize, the swoop followed two years of intelligence which linked three businesses to organised crimes including paedophilia, firearms, drug trafficking, fraud, human trafficking, prostitution and money laundering.

The three vaults contain an estimated 7,000 boxes ranging in size from A4 drawers to walk-in cupboards. Police suspect up to 90 per cent of them may contain criminal assets.

Each safe deposit box is being treated as a potential crime scene.

The enquiry, being carried out by the Met's Specialist Crime Directorate, is focused on those individuals thought to be using the premises for criminal purposes and searches are likely to take some time to complete.