British prosecutors have charged two Russian men with the nerve agent poisoning of ex-spy Sergei Skripal and his daughter Yulia in the English city of Salisbury.

The Crown Prosecution Service says Alexander Petrov and Ruslan Boshirov are charged in absentia with conspiracy to murder, attempted murder and use of the nerve agent Novichok.

Prosecutor Sue Hemming said Wednesday that the UK is not asking Moscow to extradite the men because Russian law forbids extradition of the country's citizens.

Sergei Skripal making a purchase in the Bargain Stop Store in Salisbury a few days before he was poisoned.

Police say the men, both about 40, flew from Moscow to London on Russian passports two days before the Skripals were poisoned on March 4.

Yulia Skripal was poisoned with a nerve agent just days after gaining access to a 'secret bank account'.

- AP