- Video report by ITV News Political Correspondent Paul Brand
Russia has warned Britain that "it will be sorry" over its handling over the Sergei Skripal spy poisoning.
In a stark message, Moscow's ambassador to the UN said the UK was "playing with fire" over the case.
It comes as Britain stands by its conclusion that the Kremlin is "highly likely" to have carried out the nerve agent attack on Mr Skripal, a 66-year-old former double agent.
Russia issued the threat on Thursday during a UN Security Council meeting in New York, called specifically to discuss the poisoning.
The latest remarks have plunged diplomatic relations between the two countries to a new low.
Vasily Nebenzya's warning came just hours after Mr Skripal's daughter Yulia spoke for the first time from hospital since she and her father were poisoned with Novichok, saying she was recovering.
The UN meeting had been called by Russia to discuss the handling of the case, which Moscow claims London is using to fuel an agenda of anti-Russian propaganda.
The Kremlin was also left unhappy after Britain allegedly denied it consular access to Ms Skripal.
Mr Nebenzya said the nerve agent Novichok was "not copyrighted by Russia, in spite of the obviously Russian name", adding that it was developed in "many countries".
He criticised the sources of the British intelligence services, saying reports that Russia had tested Novichok before the attack on everyday objects was "some sort of theatre of the absurd".
Mr Nebenzya said: "Couldn't you come up with a better fake story? We all know what the worth of British intelligence information is based on the experience of Tony Blair.
"We have told our British colleagues that you're playing with fire and you'll be sorry."
During his speech, Mr Nebenzya also referenced British crime series Midsomer Muders.
Mr Nebenzya also compared the Western media depiction of the poisoning to Joseph Goebbels's propaganda in Nazi Germany.
He said: "Everyone who knows crime novels, for example, the Midsomer Murders - a well-known British series - they all know hundreds of very clever ways of killing someone.
"However, those who sought to kill Sergei Skripal and his daughter supposedly chose an extremely toxic chemical substance, the most risky, dangerous method possible.
"At the same they didn't really finish the job because the two individuals seem to be alive and Yulia, thank God, seems to be improving rapidly.
"So in this very complex case there are lots and lots of questions and the further we go the more questions keep cropping up."
Earlier on Thursday, Russia's ambassador to the UK hit out at what he said was Britain's unwillingness to share information with Russia on the condition of Ms Skripal or her father.
In tit-for-tat comments, Boris Johnson earlier accused Russia of using "disinformation" and showing "shameless cynicism".
So far more than 25 countries have expelled Russian diplomats over the poisoning of the Skripals.
Moscow HAVE responded in turn by expelling 23 UK diplomats and 60 from the US.
The diplomatic crisis has led to fears that relations between the West and Russia could be entering one of its lowest points since the Cold War.