Image copyright
PA Media
A group of politicians are threatening legal action unless Boris Johnson orders an independent investigation into Russian interference in elections.
The letter signed by Green MP Caroline Lucas and Labour's Chris Bryant follows a report which said the UK "badly underestimated" the Russian threat.
The parliamentarians argue the prime minister's "lack of action" breaches the right to free elections.
The government has previously said it is "fully aware" of the threat
In July, Parliament's Intelligence and Security Committee published a long-awaited report into Russian activity in the UK including disinformation campaigns, cyber warfare and the targeting of Russian expatriates in the UK.
It claimed the government made no effort to investigate Russian interference in the 2016 EU referendum and called for "immediate action" including "an assessment of potential Russian interference" in the Brexit vote.
US intelligence chiefs have accused Russia of interfering in the 2016 presidential election and earlier this month they warned that China, Russia and Iran were among the countries seeking to influence this year's vote.
Now a group of MPs and peers in the UK say they will take the prime minister to court if he refuses to take "essential steps to protect future elections".
'Last resort'
Describing legal action as "a last resort", the letter urges the PM to "order an independent investigation of Russian interference with the democratic process from at least the 2016 EU referendum".
Ms Lucas, Green MP for Brighton Pavilion, said: "Democratic processes are clearly at risk and it seems that the integrity of our elections is being deliberately undermined."
And Mr Bryant, the Labour MP for Rhondda, said: "The government's refusal to investigate is a complete dereliction of their duty to keep us and our way of life safe."
The group also includes Labour MP Ben Bradshaw, SNP MP Alyn Smith, the Lib Dem peer Lord Strasburger and Baroness Wheatcroft, who resigned from the Conservative Party last year.
Foreign Secretary Dominic Raab has called on Russia to "desist from its attacks on the UK and our allies".
Responding to the Intelligence and Security Committee's report last month, he said the UK would be resolute in defending its democratic processes and values from "hostile states".
The Russian Foreign Ministry called the report "Russophobia".