Sergei Skripal, a former Russian spy who was poisoned by a nerve agent in Britain more than two months ago, has been discharged from hospital, England's health service said on Friday.

Sergei Skripal, 66, a former colonel in Russia's military intelligence and his daughter Yulia were found unconscious on a public bench in the southern English city of Salisbury on March 4.

Britain has accused Russia of being behind the nerve agent attack and Western governments, including the United States, expelled more than 100 Russian diplomats over the incident.

Russia has denied any involvement in the poisoning and retaliated in kind by expelling diplomats from those countries.

The Skripals were in a critical condition for weeks and doctors at one point feared that, even if they survived, they might have suffered brain damage. But their health began to improve rapidly, and Yulia, believed to be 33 years old, was discharged last month.

British military personnel work near the bench where Sergei Skripal and his daughter, Yulia, were found critically ill in Salisbury on March 4. (Matt Cardy/Getty Images)

Nick Bailey, a British police officer who responded to the incident, was also hospitalized and subsequently released.

"It is fantastic news that Sergei Skripal is well enough to leave Salisbury District Hospital," the hospital's chief executive Cara Charles-Barks said in a statement on Friday.

Security arrangement under wraps

Police said they would not discuss the security arrangements in place for the Skripals. Investigators hope their improved health will allow the Skripals to help better establish what happened in Salisbury.

A spokesperson for British Prime Minister Theresa May, who called the attack a "reckless and despicable act", welcomed Skripal's discharge.

The Russian Embassy declined to comment on Skripal's release from hospital. But Russia's ambassador to London, Alexander Yakovenko, was due to give a news conference later on Friday. He has previously requested consular access to offer assistance to Yulia Skripal since her recovery, which had not been granted. Britain said she has chosen not to take up Russia's offer of help.

Britain and international chemicals weapons inspectors have 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 denied Britain's charges of involvement in the first known offensive use of such a nerve agent on European soil since the Second World War. It has suggested Britain carried out the attack itself to stoke anti-Russian hysteria.

Sergey Skripal was convicted of spying for Britain in Moscow before coming to Britain as part of a 2010 prisoner swap.