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Published: 7:33 AM July 18, 2019 Updated: 6:25 PM September 17, 2020

Boris Johnson used a kipper as a prop in the final Tory leadership hustings to make a point about EU regulatory 'overkill' - but there was a fatal weakness in his argument.

"If you must understand why we must leave the EU, the advantages of coming out of the EU and the ability to take back control of our democracy and our own regulatory framework, I want you to consider this kipper," said the Tory leadership favourite on stage, waving the plastic-wrapped smoked fish in the air.

The prop, which he said had been handed to him by the editor of a national newspaper, allowed him to make a joke about winning back UKIP voters. But his real point was about "Brussels bureaucrats".

Johnson claimed that a kipper smoker in the Isle of Man was "utterly furious" at the costs of having to deliver his smoked fish on ice, according to what Johnson claimed was EU regulation.

Boris Johnson waves around a kipper



He explains that an Isle of Man kipper smoker is complaining about EU red tapehttps://t.co/oaTyXr72jE pic.twitter.com/QY11ZyqEui — BBC Politics (@BBCPolitics) July 17, 2019

READ: Trump-style 'Boris Blimp' unveiled for Saturday's March for ChangeThe leadership candidate described this as "pointless, expensive, environmentally damaging health and safety".

He promised that when the UK leaves the EU, we would be able to regain control over rules like these and also "do things to boost Britain's economy", although he didn't specify what.

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However, an EU spokesperson has pointed out that the requirements that Johnson described are in fact UK rules, not EU. It "falls outside the scope of EU legislation and it's purely a UK national competence", said the spokesperson.

Quite. As @GeorgeWParker points out the kipper story proves how counties outside the EU still have to apply EU rules if they want to sell into the single market. Brexit won't change that and once UK out of EU it has no say over rules https://t.co/BxpgggXlYI — Beth Rigby (@BethRigby) July 17, 2019

Critics quickly noticed another flaw in Johnson's argument: the Isle of Man is a crown dependency and is neither part of the EU or the UK. Its relationship to the EU is akin to what the UK's will be after Brexit - needing to conform to EU rules in order to have access to its market - but with no say over those rules.

The new Tory leader will be announced on Tuesday.