The nerve agent used to kill former Russian intelligence office Sergei Skripal, 66, in Salisbury may have been planted in his daughter Yulia's luggage before she left Moscow, a senior intelligence source has said.
A senior intelligence source told The Daily Telegraph they believe an item of clothing, cosmetics or a gift may have been laced with the Novichok agent used to poison the spy and his daughter almost two weeks ago.
It would mean that the would-be assassin may have never entered the UK, making the hunt to catch them even more difficult.
33-year-old Yulia lives in Moscow, but is believed to have flown to the UK to visit her father the day before the attack.
Garry Collins, 63, who had been Mr Skripal's driver since 2011, told The Times that the Russian had told him about his daughter's travel plans. "He said Yulia was arriving on Saturday afternoon and had planned a two-week visit."
Mr Skripal and his daughter spent the afternoon in Salisbury, and had lunch at Zizzi's Italian restaurant before they were found in a park shortly after 4pm on Sunday, barely 24 hours after she is believed to have arrived in the country.
Deputy Chief Constable Paul Mills of Wiltshire Police said that as many as 131 people may have come into contact with the nerve agent before the alarm was raised.
Prime Minister Theresa May expelled 23 Russian diplomats from the UK this week in response to the attack, claiming they were undeclared intelligence agents.
Valdimir Putin's spokesperson vowed that a Russian response to the diplomatic expulsion "could come at any minute".
Whilst Russian Foreign Minister Sergei Lavrov said Russia "will, of course" expel British diplomats from Russia in response.