The oil giant spent 40pc of its almost $1bn worldwide security budget between 2007 and 2009 on protecting staff and buildings in the volatile African region, the Guardian claimed, citing leaked internal data.

Shell also allegedly maintains a 1,200-strong internal police force in Nigeria, plus a network of plainclothes informants.

“The scale of Shell’s global security expenditure is colossal,” Ben Amunwa of London-based oil watchdog Platform told the newspaper.

The documents suggest that Shell’s worldwide security costs almost doubled in the three-year period, coinciding with the rise of armed insurgency in the Niger delta.

In 2008, 62 Shell employees or contractors were kidnapped and three killed in the region.

In the same year, $99m was spent on “third parties” for security. This was twice as much as what the company spent on its own security staff and is believed to include the services of 600 Nigerian government police and 700 members of the controversial state “joint task force” (JTF) comprised of army, navy and police, the Guardian claimed.

Shell denies having any direct control over JTF forces.

“Protecting our people and our assets is Shell’s highest priority,” the company said. “Our spending on security is carefully judged to meet this objective, wherever we operate in the world. We have always acknowledged the difficulties of working in countries like Nigeria. In the period that this report refers to, the armed militancy in the Niger delta was at its height, requiring a relatively high level of security spending there.”