Why have Britain and its Nato allies been unable to deter Russian President Vladimir Putin from acts like spreading a deadly nerve agent in a peaceful British city? Ask Jeremy Corbyn.

When confronted with the British government's conclusion that Russia was responsible for what amounted to a military attack on his country, the opposition Labour Party leader and his spokesman (a) refused to accept that the Kremlin was responsible; (b) cast doubt on British intelligence; (c) complained that Moscow had not been accorded due process and; (d) said the right response was "robust dialogue".