Plans to scrap most tariffs on imports after a no-deal Brexit – threatening huge job losses in UK firms – will be kept secret until it becomes a reality, the business secretary says.

Greg Clark refused, multiple times, to deny that up to 90 per cent of levies would be removed, on everything except cars, in agriculture and on some textiles.

The looming decision has already been criticised as “the ultimate Brexit betrayal” by a trade union and “extraordinarily damaging” by Labour.

The long-promised schedule has been approved by a cabinet committee, but Mr Clark said it would be kept under wraps unless the UK was definitely set to crash out of the EU without an agreement.

Asked when it would be published, Mr Clark said: “Once we knew that we were leaving without a deal on the 29th of March.”

The delay has been attacked as “amazingly negligent” by the respected Institute for Government, which said it would not “go down well with business and farm organisations”.

The government confirmed last month that scrapping tariffs is among “all options” being considered if a no-deal becomes a reality.

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Ministers fear failing to slash duties would sent prices soaring in the shops and hit UK producers who depend on supply chains from the EU.

But, because tariffs are a charge on thousands of types of goods entering the country, they protect domestic producers from competitors around the world.

Sky News has been told that only the 10-20 per cent of the most sensitive items would retain their protection, including cars, beef, lamb, dairy and some lines of textiles.

However, the vast majority of tariffs, including those on the component parts used to make cars, many finished food products and even some farm produce, including cereals, would be eliminated entirely.

Quizzed by BBC Radio 4, Mr Clark said the schedules would only be published if, after next week’s Commons votes, MPs have backed a no-deal departure.

“We have been consulting with different industry sectors on this. It has big implications for different sectors,” he admitted.

“Ceramics is an industry that I know very well. It has been subject to very unfair competition, to dumping of very cheap ceramic exports from the Far East, from China.”

Industry leaders fear being undercut by competition from emerging economies, such as China and Brazil, from which – unlike EU imports – tariffs are currently levied.

Labour has also protested that zero tariffs would leave the UK with “nothing to negotiate with” in future trade talks, because other countries would already have the prize they would seek