By Alistair Smout and Guy Faulconbridge

LONDON (Reuters) – Former Russian spy Sergei Skripal is no longer in a critical condition and his health is improving rapidly more than a month after he was poisoned with a nerve agent in England, the British hospital treating him said on Friday.

Skripal, 66, a former colonel in Russian military intelligence who betrayed dozens of spies to Britain’s foreign spy service, and his daughter Yulia were found slumped unconscious on a public bench in the English city of Salisbury on March 4.

Britain blamed Russia for the poisoning, the first known offensive use of such a nerve agent on European soil since World War Two. Moscow denied any involvement and suggested that Britain had carried out the attack to stoke anti-Russian hysteria.

“He is responding well to treatment, improving rapidly and is no longer in a critical condition,” Christine Blanshard, Medical Director at Salisbury District Hospital, said in a statement.

British Prime Minister Theresa May said the Skripals were poisoned with Novichok, a deadly group of nerve agents developed by the Soviet military in the 1970s and 1980s.

Russia has said it does not have such nerve agents and President Vladimir Putin said it is nonsense to think that Moscow would have poisoned Skripal and his 33-year-old daughter.

A British judge said last month, nearly three weeks after the attack, that it might have left them with compromised mental capacity and that it was unclear whether they would recover.

The attack prompted the biggest Western expulsion of Russian diplomats since the height of the Cold War as allies in Europe and the United States sided with May’s view that Moscow was either responsible or had lost control of the nerve agent.

But Moscow has hit back by expelling Western diplomats, questioning how Britain knows that Russia was responsible and offering its rival interpretations, including that it amounted to a plot by British secret services.

Both Moscow and London have accused each other of trying to deceive the world with an array of claims, counter-claims and threats.

“PLAYING WITH FIRE”

At a session of the executive of the global chemical weapons watchdog this week, Russia called for a joint inquiry into the poisoning of the Skripals, but lost a vote on the motion.

At a UN Security Council meeting on Thursday, Russia warned Britain that “you’re playing with fire and you’ll be sorry” over its accusations.

Given the twists and turns in the affair, British and Russian diplomats have variously claimed the mystery to be worthy of Sherlock Holmes or of an Agatha Christie whodunit.

In an exchange at the United Nations, the ambassadors of Britain and Russia quoted extracts from “Alice in Wonderland” at each other.

The hospital in Salisbury said it was providing the medical update in response to “intense media coverage yesterday.”

Russian state television reported that Yulia had phoned her cousin in Russia and told her that she and her father were both recovering and that she expected to leave hospital soon.

Yulia’s health has improved rapidly. On Thursday, she issued a statement through British police to thank hospital staff and people who came to her help when “when my father and I were incapacitated”.

Sergei Skripal, who was recruited by Britain’s MI6, was arrested for treason in Moscow in 2004. He ended up in Britain after being swapped in 2010 for Russian spies caught in the United States.

Since emerging from the John le Carre world of high espionage and betrayal, Skripal lived modestly in Salisbury and kept out of the spotlight until he was found poisoned.

British police believe a nerve agent was left on the front door of his home. Skripal’s cat was put down by British authorities. His guinea pigs were discovered dead.

“When a vet was able to access the property, two guinea pigs had sadly died,” a British government spokeswoman said.

“A cat was also found in a distressed state and a decision was taken by a veterinary surgeon to euthanise the animal to alleviate its suffering,” the spokeswoman said.

(Editing by Richard Balmforth)