Downing Street was forced to come to the defence of the foreign secretary Boris Johnson after he warned the French president, François Hollande, not to respond to Brexit by trying to “administer punishment beatings” in the manner of “some world war two movie”.

The foreign secretary evoked the darkest period of France’s recent history as he rejected comments by an adviser to Hollande who said Britain should not expect a better trading relationship outside Europe than it currently enjoys inside.

At a foreign policy conference in Delhi, Johnson said: “If Hollande wants to administer punishment beatings to anybody who seeks to escape [the EU], in the manner of some world war two movie, I don’t think that is the way forward. It’s not in the interests of our friends and partners.”

His words came only 24 hours after Theresa May reminded her cabinet ministers in her Lancaster House speech to show restraint by warning “any stray word” could make securing a Brexit deal more difficult.

Although the French government declined to respond to Johnson’s remarks, Guy Verhofstadt, the lead Brexit negotiator for the European parliament, branded them “abhorrent and deeply unhelpful”.

British politicians accused Johnson of being unfit to head the diplomatic service. Tim Farron, the Liberal Democrat leader, said: “This is an utterly crass and clueless remark from the man who is supposed to be our chief diplomat.

“I assume Boris Johnson says these things to deflect from the utter shambles this Brexit government is in over its plans to take Britain out of the single market. But this kind of distasteful comment only serves to unite Europe further against Britain at a time we need friends more than ever.”

Jeremy Corbyn’s spokesman said: “We’re well aware the foreign secretary has a habit of making wild and inappropriate comments, and talking about world war two in that context is another one of those.

“That’s not going to be something that’s going to improve the climate for these negotiations. I don’t think threats or wild comparisons or analogies are going to help the situation.”

But Downing Street defended the foreign secretary, saying he had not likened Hollande to a Nazi, and was only “making a theatrical comparison to some of those evocative WWII movies”. The spokeswoman rejected press interpretations of the comments, comparing them to the “hyped-up media reports” condemned by the prime minister in her Brexit speech.

Jo Johnson, the universities and science minister, said his brother had been “using colourful language to get over an important point”. Michael Gove, Johnson’s fellow leave campaigner, said people offended by Johnson were “humourless [and] deliberately obtuse”.

The foreign secretary’s remarks in Delhi came after Jacques Audibert, diplomatic adviser to Hollande, said that Britain could not expect to get a better deal outside the EU than it enjoyed inside. Some ministers believe France is leading the calls to punish the UK, and possibly the City of London, over its plans to leave the European Union.

Last October Hollande, in common with many other European politicians in recent months, declared Britain had to pay a price for Brexit: “There must be a threat, there must be a risk, there must be a price,” he declared.

Johnson’s remarks are likely to add to growing diplomatic friction between France and the UK following a public feud over the wisdom of France calling a Middle East peace conference just before Donald Trump takes power in the US. The UK refused to send a delegation to the conference and did not sign the final communique.

It is not the first time the former London mayor has evoked the second world war in the context of Brexit. He told the Sunday Telegraph during the referendum campaign that the EU was an attempt “by different methods” to unite the continent under a single government. He said: “Napoleon, Hitler, various people tried this out, and it ends tragically.”

Interviewed on BBC Radio 4’s Today programme on Wednesday, the Brexit secretary David Davis cited the “difficult histories” of other EU nation states as evidence for why they would not want to leave the EU.

Davis also quoted the former cabinet secretary Robin Butler who, he said, had told him: “The civil service coped with world war two; they can cope with this.”

“There is no other country which is in our position,” he said. “We are an offshore island. We have got a great global history and so on. For us, going into the EU in the first case it was the common market, we saw it as an economic issue. But for most of the countries of Europe it is not just about economics. It is about democracy. It’s about the rule of law – countries that have come from difficult histories into what for them is the exemplar of modern politics – freedom, rule of law, democracy.”

Speaking on Wednesday, Johnson said new tariff barriers between Britain and Europe would “cut both ways”, citing imports of German luxury cars into Britain. It was “absolutely incredible”, he said, “that in the 21st century member states of the EU should be seriously contemplating the reintroduction of tariffs or whatever to administer punishment to the UK”.

He said: “[Britain] can put a 10% tariff on 820,000 cars, Mercs. That’s a lot of money for the exchequer. We think we can do a great free-trade deal for the benefit of both sides. The more trade, the more jobs on both sides.”

He added that it would be “foolish for the EU to seek to cut off its nose to spite its face by punishing the City of London [because] those jobs won’t migrate to Paris or Frankfurt but to Singapore or Hong Kong or New York”.

As a result, he said, they were not going to be tempted to leave the EU.

Johnson told the audience in the Indian capital it was “time to stick up for free trade”, arguing that Britain and India had enormous potential to boost their economic ties, and suggesting the Indian government start by relaxing its 150% tariff on imported whisky.

Scotch whisky accounts for about 4% of the Indian market, the largest market for the liquor in the world. “Now imagine we could just double that or treble that by removing those pesky tariffs, giving the Indian consumer more money to spend on other things,” he said.

“And, symmetrically, we could have zero tariffs on wonderful Indian products like those electric cars or buses or perhaps even bicycles that we’re now seeing on the streets of London.”

Such a deal could not be negotiated until Britain formally left the EU, he said, but could at least be “sketch[ed] out in pencil on the back of an envelope”.

“We may be leaving the EU, we may be taking back control of our borders, but that does not mean we want to haul up the drawbridge. We do not want to deter Indian talent from our country,” he said.