Vladimir Putin has gone "full tonto", Ben Wallace, the Defence Secretary, said on Wednesday as the Government hardened its rhetoric over the Russian president.

       Mr Wallace also said the Scots Guards – of which he used to be a part – had "kicked the backside" of Russia in the Crimean War and "can always do it again".

       His remarks came a day after Boris Johnson told MPs that Mr Putin was showing an "illogical and irrational frame of mind" and had voiced "absurd" reasoning to justify invading Ukraine.

       Asked on Wednesday whether Mr Putin was "insane", the Prime Minister's spokesman said he would not give a "clinical assessment".

       Foreign policy commentators have questioned whether Mr Putin is behaving irrationally after he ordered troops into eastern Ukraine.

       Mr Wallace was filmed making his comments as he talked to serving military personnel at the Horse Guards building in Westminster.

       He said: "It's going to be a busy Army. Unfortunately we've got a busy adversary now in Putin, who has gone full tonto."

       The Defence Secretary added that the UK has 1,000 personnel on standby to respond to the crisis, adding: "The Scots Guards kicked the backside of Tsar Nicholas I in 1853 in Crimea – we can always do it again. Tsar Nicholas I made the same mistake Putin did. He had no friends, no alliances."

       His remarks were made in a room dominated by a large painting depicting the Battle of Inkerman, a major engagement during the Crimean War, which took place between 1853 and 1856. The war saw Russian forces defeated by an alliance that included the UK, France and the Ottoman Empire.

       Mr Wallace, a former Scots Guards officer, recently topped a poll of Tory members on the most popular Cabinet minister