A copy of the letter was sent to Cressida Dick, the commissioner of the Metropolitan Police; Andrew Parker, the director-general of MI5; and the foreign secretary, Boris Johnson.



Cooper said in a statement: "I welcome the Home Secretary’s decision to look again at other cases where questions have been raised. Rightly, the government is focused on the current investigation into the attack in Salisbury and supporting the efforts of the police, as well as responding to the incredibly serious conclusion the Prime Minister announced in the Commons yesterday.

"But given the gravity of these issues, it is also right that the authorities should reassure us that they have looked at any further allegations or relevant evidence put forward in any other cases. As the Home Secretary has said in her letter, the government must satisfy itself that the correct finding was reached in each case and the public need to know that relevant questions about wider Russia links have been investigated and answered."

After the poisoning of former Russian spy turned defector Sergei Skripal and his daughter, Yulia, in Salisbury on 4 March, Lord Ian Blair, the former commissioner of the Met, said he backed Cooper's call for an investigation into the 14 suspicious deaths.

Lord Blair was in charge of the Met in 2006 when former Russian spy Alexander Litvinenko was killed with radioactive poison. An inquiry 10 years later concluded that the murder was probably the work of Russian secret service agents acting on the orders of Vladimir Putin.

The Russian embassy in London responded to the suggestion in various reports that prime minister Theresa May is considering launching a cyberattack on Russia, if the Skriapl case is found to be linked to the Russian state.

"Statements by a number of MPs, 'Whitehall sources' and 'experts' regarding a possible 'deployment' of 'offensive cyber-capabilities' cause serious concern. Not only is Russia groundlessly and provocatively accused of the Salisbury incident, but apparently, plans are being developed in the UK to strike Russia with cyber weapons.

"Judging by the statements of the Prime Minister, such a decision can be taken at tomorrow’s meeting of the National Security Council. We invite the British side to once again consider the consequences of such a reckless move."

Also on Tuesday, the British broadcasting regulator warned Russia Today, the Kremlin-backed news channel which has offshoots in the US and in the UK, that it could face losing its licence to broadcast if Russian state involvement was proven in the Skripal case. Ofcom is investigating whether RT is a "fit and proper" broadcaster as defined by the broadcasting code.

In response to this, Russia Today said in a statement: "We disagree with the position taken by Ofcom; our broadcasting has in no way changed this week, from any other week and continues to adhere to all standards.

"By linking RT to unrelated matters, Ofcom is conflating its role as a broadcasting regulator with matters of state. RT remains a valuable voice in the UK news landscape, covering vital yet neglected stories and voices, including those of the many MPs and other UK public figures who have been shut out of public discourse by the mainstream media."