The company says that other countries including Botswana, South Africa, Namibia and India should verify diamonds as non-Russian on behalf of the G7 and EU.

Intense lobbying over the new rules threatens to delay the certification scheme altogether.

Ms Wade-Smith is banned from lobbying British officials under the government’s business appointment rules, but has been in contact with other governments since starting the position in February.

An industry insider said her role in the US and former position as Britain’s trade commissioner to Africa had given her extensive government contacts relevant to the diamond trade.

The De Beers proposal to widen the certification scheme is favoured by diamond companies on the World Diamond Council and some African producers.

But experts say that handing the enforcement of the ban to other countries who have not signed up to it could lead to more Russian diamonds entering the West illegally.

Hans Merket, an expert in the diamond trade and researcher for the International Peace Information Service, said that if the lobbying is successful, it could create “weak links in the chain”.

“Agreeing on shared objectives presents the biggest challenge, given that countries such as Botswana, South Africa, and India do not align with the G7’s focus on sanctioning Russia,” he told The Telegraph.

“The problem is that without agreement on the ultimate objective of controls, allowing additional countries to verify the origin of the diamonds risks creating weak links in the chain that are prone to exploitation by those seeking to flout traceability requirements.”

He added that the solution favoured by the diamond companies was “based on trust rather than evidence and therefore leaves much more room for manipulation”.