The presenter of a Russian government-controlled TV news programme has made what appears to be a veiled threat to anyone thinking of being a double agent for Britain.

'I don't wish death on anyone, but for purely educational purposes, I have a warning for anyone who dreams of such a career,' Kirill Kleimenov, presenter of Channel One's flagship Vremya news programme said.

'The profession of a traitor is one of the most dangerous in the world,' Kleimenov was reported by the BBC as saying, pointing out that the few who had chosen it had lived to a ripe old age.

Kirill Kleimenov, presenter of Channel One's flagship Vremya news programme, said few traitors lived to old age and that it was not a good idea for them to go to Britain

Sergey and Yulia Skripa are both in a critical condition in hospital

An intensive police investigation is continuing in Britain into the circumstances of the attack on Mr Skripa and his daughter

The presenter said that excessive drinking, drug addiction, stress and depression leading to heart attacks and even suicide were the 'professional illnesses of a traitor'.

He also had what appeared to be a threatening piece of advice for 'traitors or those who simply hate their country in their free time'.

'Don't choose Britain as a place to live,' he warned.

One Russian-based London correspondent was strongly critical of Boris Johnson's response to the crisis,accusing him of behaving like 'an infant in a man's suit'

'Something is wrong there. Maybe it's the climate, but in recent years there have been too many strange incidents with grave outcomes there.'

The remarks were noticeably different from the rest of the evening's coverage, which mirrored the denials and bemusement of Russian state media.

On NTV - ultimately controlled by state gas company Gazprom - a presenter said the Western media were accusing Russia of poisoning Mr Skripal despite the absence of any evidence, the BBC reported.

Its London correspondent, Liza Gerson, alluded to Britain's Porton Down research facility in the investigation, pointing out that it tested chemicals used against German soldiers in World War One.

The journalist was also critical of Boris Johnson's warning to Russia this week, saying the Foreign Secretary was known for his 'unpredictable antics' and was 'an infant in a man's suit'.

Meanwhile a presenter of state channel Rossiya 1 accused the British authorities of not even trying to seek Russia's co-operation in the investigation, 'but have already discovered a Russian trace in the case', the BBC said.

On Thursday the British investigation into the poisoning of Sergei Skirpal, 66, and his daughter Yulia, 33, continued with police extending the cordon around his Salisbury home and the surrounding street to 150 yards.

Officers have now confirmed 21 people, including Mr Skirpal, his daughter, and Sgt Bailey, were treated in hospital in relation to the attack, after previously claiming the number was 'fewer than 10'.