FREE now and never miss the top politics stories again. SUBSCRIBE Invalid email Sign up fornow and never miss the top politics stories again. We will use your email address only for sending you newsletters. Please see our Privacy Notice for details of your data protection rights.

It also said two named individuals had made a successful departure. This and an earlier intercept form a key part of Britain’s intelligence evidence against Russia over the Skripal poisonings, sources said last night. Insiders said the two messages were intercepted by RAF analysts stationed at a listening post in southern Cyprus.

PH VITAL CLUES: Yulia Skripal with her father Sergei, a former Russian spy now living in Britain

On the day of the poisonings, March 4, one was sent from a location near Damascus in Syria to “an official” in Moscow including the phrase ‘the package has been delivered” and saying that two individuals had “made a successful egress”. This prompted a young Flight Lieutenant to recall a separate message that had been intercepted and discounted on the previous day. What it said has not been revealed but sources say it became relevant once the Skripals were attacked. The intercepts were automatically shared with the Government communications headquarters GCHQ in Cheltenham.

They are understood to have formed “just one part” of the intelligence packet which later allowed Prime Minister Theresa May to state it was “highly likely” that Russia was behind the attacks. They emerged as Russia’s embassy in London called for a meeting between its ambassador, Alexander Yakovenko, and Foreign Secretary Boris Johnson “in order to discuss the whole range of bilateral issues, as well as the investigation of the Salisbury incident”. The offer was described by the Foreign Office as “a diversionary tactic”. The Skripals are believed to have been poisoned with nerve agent Novichok but are now recovering in hospital.

Yulia, 33, who was on a visit to her father from Moscow, revealed last week she had recovered from her coma a week ago and “my strength is growing daily”. Her 66-year-old father, who lives in Salisbury, is said to be no longer critically ill. The intercepts were divulged to the US where President Donald Trump had been criticised for telephoning Russian President Vladimir Putin on March 20 to congratulate him on his electoral success without mentioning the nerve agent attacks. Just six days later he announced the expulsion of 60 Russian diplomats from the US because of the Skripal case.

PH Yulia was on a visit to her father from her home in Moscow when they were poisoned

Alex Younger, the head of MI6, is said to have personally sent a “well done” message to the RAF signals unit. A source said: “An RAF intelligence gathering station in Cyprus intercepted a communication from a Russian on the morning of March 4. “Although details of the intercept are classified, one part of the message, which was sent to an official in Moscow, stated that ‘the package has been delivered’. “During a routine trawl through the previous 24 hours’ intercepts, an RAF Signals Intelligence Officer alerted a senior officer to another electronic message, which had been spotted the previous day.

“Given the events of that Sunday, that previous intercept was deemed tangentially relevant as well.” Foreign ministries of allied nations have told how they were originally offered a small amount of evidence in the days following the attack at embassy level. A fuller briefing was provided on March 23 by, among others, Britain’s national security adviser Sir Mark Sedwill, at the heads of state meeting in Brussels on March 23. Evidence against Russia falls broadly into two categories.

The first relates to the Novichok itself. British intelligence is believed to have established that the weapons grade nerve agent was manufactured in Russia’s Scientific and Research Institute of Radiation and Chemical Defence in Shikhany, about 620 miles south-east of Moscow. A report, shown to the US and other allies, suggests that small amounts of the chemical compounds used in the attack were tested at Shikhany over the past decade in an apparent effort to develop an assassination weapon. Experts say that, in the case of the Skripal poisonings, as little as five millilitres of the nerve agent was all that agents would have needed.

The second tranche of evidence relates to human intelligence gained by the secret services and electronic intelligence. News that Mr Skripal was recovering could have prompted the invitation yesterday from the Russian Ambassador Yakovenko to Mr Johnson. In a statement posted on its website, the Russian embassy said: “We believe that it is high time to arrange a meeting between ambassador Alexander Yakovenko and Foreign Secretary Boris Johnson in order to discuss the whole range of bilateral issues, as well as the investigation of the Salisbury incident.” The Foreign Office said it would “consider the request and respond in due course” but accused Russia of “pursuing a different diversionary tactic”.

Russia spy poisoning: Latest pictures after Sergei Skripal puts Salisbury on lockdown Thu, March 8, 2018 Russia spy poisoning: Latest pictures after Sergei Skripal puts Salisbury on lockdown. Play slideshow PA 1 of 20 Personnel in hazmat suits secure a tent covering a bench in Salisbury's Maltings shopping centre

It said: “It is Russia’s response that has been unsatisfactory. “It is over three weeks since we asked Russia to engage constructively and answer a number of questions relating to the attempted assassinations of Mr Skripal and his daughter.” Last night Professor Anthony Glees, head of Buckingham University’s Centre for Security and Intelligence Studies, said: “All the different versions of this event that Moscow has put out show that they treat Britain with contempt. In my view, this overture is a further step in this policy. “It may well be that Russia, now that it sees the Skripals are making a full recovery, may want to ramp things back. “Our Government has put Russia in the dock of world history over the Salisbury poisonings.”

Anna Chapman in pictures: Russian spy swapped for poisoned Sergei Skripal Tue, March 6, 2018 Anna Chapman in pictures: Russian spy swapped for poisoned Sergei Skripal. Play slideshow Getty 1 of 11 Russian spy Anna Chapman in pictures

International backing for Britain against Russia over the Sergei Skripal poisoning remains firm and resolute, senior foreign diplomats said last night. More than 150 Russian diplomats have been expelled from 28 countries in Europe and beyond in a move of unprecedented solidarity. Last night many revealed that they had been persuaded to act by Theresa May’s “powerful argument”, their own intelligence of Russian activity and “Russian form”, such as the annexation of Crimea and the downing of Malaysia Airlines flight MH17. While Britain made it known that it possessed evidence, backing by many countries had already been offered more than a week before the full intelligence picture was revealed at a heads of state meeting in the European Council on March 23. Speaking last night, Polish deputy minister Bartosz Cichocki told how he was briefed by British officials in Warsaw in the days following the March 4 assassination attempt.

“We were presented with evidence about the case and asked whether we’d be ready to participate in a demonstration of solidarity. “We responded very quickly. In our case, the depth of the UK’s information wasn’t critical because we had been observing patterns of Russian behaviour and what happened in Salisbury fitted into that precisely. “We did not request that the UK presented everything at that early stage. It was obvious Britain had submitted the case to the Organisation for the Prohibition of Chemical Weapons in The Hague, so we knew there would be an international investigation. "It wasn’t necessary to prolong political decisions for the months it will probably take for OPCW experts to investigate.”

He added: “We understood this was not just a bilateral issue between Russia and Britain but rather about the security of citizens in Europe. “It’s important to note that every country which reacted in support had been targeted, in this way or another, by Russia in the past. The overwhelming feeling was ‘enough’. Salisbury was a catalyst.” On Tuesday, Gary Aitkenhead, chief executive of the Government’s Defence Science and Technology Laboratory at Porton Down, revealed they were not yet able to prove that the military-grade Novichok nerve agent came specifically from Russia. That fact was seized upon by the Kremlin.

But deputy minister Cichocki said: “Russia’s response has been typical of its behaviour. It denies, it sends troops in uniform without insignia, it uses hackers and internet trolls. We gave Russia enough time to demonstrate goodwill and transparency and it failed to do this. “There is always a way for it to deny everything but allowing us to be fooled by this would risk the lives of our citizens. The time comes to be less bureaucratic and to take action, once we know who is responsible. In this case, we have no doubt that Russia was responsible.” He said that the mass expulsion of diplomats was significant. “We expelled four but the expulsion of 150 by so many countries is unprecedented.

“We have already seen Russia try to drive a wedge against this unity, so we need to constantly work on it.” The views were echoed by the Czech Republic, which expelled three Russians, and Estonia which expelled one “high-level operative”. Jakub Durr, the Czech Republic’s deputy foreign minister for European issues, said he trusted the materials and evidence from the UK. “We also have particle data and intelligence. But when it comes to the UK position, we completely trust our British partner. "You don’t doubt your friend, especially when the argument is supported by a phrase like ‘highly likely’ which, in diplomatic terms, says much.