Russian President Vladimir Putin wished "good health" to former agent Sergei Skripal as he was released from a British hospital Friday, after recovering from a nerve agent poisoning alleged to have been orchestrated by the Kremlin.

"God grant him good health," Putin said in a Sochi press conference with German Chancellor Angela Merkel.

"If a military-grade poison had been used, the man would have died on the spot. Thank God he recovered and that he left (hospital)."

Russia has rejected British accusations of involvement in the poisoning, which sparked a diplomatic crisis that saw Russia and the West expelling dozens of diplomats in tit-for-tat moves.

Skripal and his daughter Yulia, who was visiting from Moscow, collapsed on March 4 on a bench in Salisbury, the city in southwestern England where the former double agent lives.

Police officer Nick Bailey who came to help was also taken to hospital. He was discharged several weeks after the attack, while Yulia Skripal was treated in hospital for just over a month.

Salisbury District Hospital nursing director Lorna Wilkinson said looking after Skripal and the two others poisoned by the same nerve agent had been "a huge and unprecedented challenge".

"This is an important stage in his recovery, which will now take place away from the hospital," she said.

Souring relations

Britain has said the poisoning was carried out with a type of nerve agent known as Novichok which was developed in the Soviet Union.

UN experts have confirmed that a high-purity nerve agent was used without specifying whether it was Novichok or saying who might be behind the poisoning.

Following Skripal's release, the Metropolitan Police said it was making "good progress" in the case.

"This is a complex investigation and detectives continue to gather and piece together all the evidence to establish the full facts and circumstances behind this dreadful attack," it said in a statement.

Russia has challenged Britain to provide evidence in the case.

"We have several times offered our British partners any necessary assistance in the investigation (of the poisoning)," Putin said Friday.

"So far we have received no response. Our offer remains open."

Protective custody?

The Russian embassy in London accused Britain of blocking access to the pair in defiance of diplomatic convention, airing the claims in a set of sensational social media posts.

The Foreign and Commonwealth Office said their offer of consular assistance had been passed to Yulia Skripal but that she had turned it down.

Both she and her father are now likely to be in protective custody.

"In the interests of Sergei and Yulia's safety, we will not be discussing any protective or security arrangements that are in place," the Metropolitan Police said.

Skripal is a former Russian military intelligence officer who passed information on Russia's agents in Europe to British security services, resulting in imprisonment in his homeland.

He moved to Britain as part of a spy swap in 2010 and has lived there ever since.