Gavin Williamson’s boast that Brexit could “enhance the UK’s lethality” is the latest in a string of naive forays by the 42-year-old defence secretary. He may have intended it as a boost to Britain’s global military standing but it is more likely to just confirm Williamson’s reputation as the cabinet’s Private Pike, the hapless youth in the sitcom Dad’s Army.

In his first 15 months in the job Williamson’s antics have regularly invited the Captain Mainwaring response of “Stupid boy!”

In March, in the wake of the poisoning of the former Russian spy Sergei Skripal and his daughter Yulia in Salisbury, Williamson had a message for the chief suspects. “Frankly, Russia should go away and should shut up,” he said in remarks that were widely ridiculed in both Russia and the UK.

Play Video 0:25 Gavin Williamson tells Russia to 'go away and shut up' - video

Challenged by ITV about those comments, Williamson compounded the error by repeatedly refusing to answers questions about his informal use of language. Williamson stonewalled so blatantly that presenter Richard Madeley terminated the interview.

Play Video 2:18 Richard Madeley cuts off Gavin Williamson after he repeatedly dodges question on Russia – video

In July, Williamson earned the dubious distinction of becoming the first minister to be heckled by his own phone at the dispatch box in the House of Commons. Discussing Syria appeared to prompt the Siri service on his iPhone. It chirped up with this interruption: “I’ve found something on the web for Syria…”

Play Video 0:35 Gavin Williamson 'heckled' by Siri during Commons speech – video

Struggling with new technology has been something of a theme of Williamson’s gaffe-prone time in office. His use of the photo-sharing site Instagram landed him in more trouble. In November Williamson was ticked off by the parliamentary authorities for breaching rules about photography in the Commons when he posted a picture of his boss Theresa May making a statement to MPs about Brexit.

And the content of his prosaic Instagram posts, featuring dreary constituency shots, animals and even a tribute to the value of his new garden incinerator, have also been widely mocked. Beside an underwhelming picture of his 1981 Land Rover Defender, Williamson wrote that it epitomises everything that is so fantastic about #greatbritain. He had apparently forgotten that Land Rover has been owned by India’s Tata Motors for more than a decade.

British ‘lethality’? Gavin Williamson’s brain has gone absent without leave | Simon Jenkins Read more

Last summer, senior figures in the defence department were reported to be exasperated by some of Williamson’s eccentric suggestions for stretching the defence budget. According to the Sun, he put forward the idea of mounting guns on tractors as makeshift mobile missile launchers, and buying secondhand ferries to convert them to beach assault craft. A source told the Sun: “The man is out of his mind. No one knows what to do.”

He even tried to launch his own set of medals for gallantry, apparently oblivious to the fact that only the Queen can approve such honours.

To the incredulity of his staff, Williamson was at it again before Christmas when he proposed firing paintballs to deter Spanish ships from trespassing in Gibraltar’s waters. During a regular Ministry of Defence meeting with senior armed forces staff, he suggested that Gibraltarians could be armed with paintball guns to fire at passing Spanish ships to scare them off. In response the chief of defence staff, Gen Sir Nick Carter, simply rolled his eyes, according to the Sun.