A former Russian spy found unconscious in the quiet English city of Salisbury was deliberately targeted with a nerve agent, according to British police.

The attack on Sergei Skripal and his daughter has also left one British officer in hospital in a serious condition. Police have declined to name the substance used, but the attack has drawn immediate comparisons to the murder of Alexander Litvinenko, another former spy who died in 2006 after having Polonium-210 slipped into his tea.