Russian President Vladimir Putin on Friday wished former spy Sergei Skripal "good health" after he was discharged from a British hospital following his poisoning in March.

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

"We have several times offered our British partners any necessary assistance in the investigation (of the poisoning). So far we have received no response. Our offer remains open," he said.

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.

The poisoning sparked a diplomatic crisis that saw Russia and the West expelling dozens of diplomats in tit-for-tat moves.

Britain has accused Russia of being behind the poisoning, saying it was caused by a type of nerve agent known as Novichok which was developed in the Soviet Union.

Moscow has furiously denied the claim, suggesting at various points it has been set up by British security services.