Amazon has been accused of aiding bomb makers as the former head of the CIA said that social media companies must take a share of the blame for the London Underground bucket bomb.

The online retail giant was found to group together key components needed to create explosives under the “frequently bought together” tab. Whilst many of the ingredients are innocent on their own, together they can be used to create explosives or devices.

When buying a certain chemical on Amazon the ingredients are offered to make black powder. The “customers also bought tab” also offered steel ball bearings, push button switches and battery connectors and cables.

Ignition systems and remote detonators are also available on the website, the Channel 4 News investigation found.

The news came just hours before a report was released in which General David Petraeus said that Google, Twitter and Facebook are failing to tackle online extremism as it emerged jihadist content gets more online traffic in Britain than any other European country.

The former head of the CIA, who wrote the forward to a report published by Policy Exchange calling for a new regulator with the power to fine companies, said the Parsons Green terror attack in London last week “using a device that can be built from instructions available online – merely underscored once again the ever-present nature of this threat”.