Skripal 'regretted being double agent'
A former classmate says the spy told him he wrote to Vladimir Putin asking to come back to Russia.
Sergei Skripal and his daughter Yulia are in a critical condition after being poisoned by a nerve agent in Salisbury on 4 March.
Vladimir Timoshkov was speaking exclusively to the BBC.
Video produced by Abdujalil Abdurasulov and Elizaveta Vereykina.