Mr Skripal, 66, and his 33-year-old daughter, Yuli are fighting for their lives in hospital after falling ill in the Wiltshire city on Sunday.
"It's not yet clear whether this poisoning was state-sponsored, or whether it was carried out by a faction who are trying to flex their muscles.
"But Putin is popular in Russia because he's seen as a very strong figure. Part of the reason for this perception is that, under his leadership, traitors can't escape, they're never safe."
The Foreign Secretary also said the UK would respond "robustly" if it there was state involvement.
But the Russian embassy hit back, saying it was "completely untrue" to suggest the country's special services were involved.
An embassy spokesman also criticised Mr Johnson for speaking "in such a manner as if the investigation was already over".
Mr Skripal was convicted in 2006 of passing state secrets to MI6 before being given refuge in the UK as part of a spy swap in 2010.
This article was originally published by the Daily Express on 7 March 2018 and can be viewed online here.
Ben Keith is ranked in Chambers and Partners as a band 1 leader in the field of Extradition at the London Bar. Ben is also ranked in the Legal 500 as a band 1 leading individual in international crime and extradition at the London Bar.