A UK-US trade agreement that will reduce tariffs on cars, steel and aluminium may not be in place for weeks in a major blow to British industry, officials have admitted.

It means those industries continue to face 25 per cent levies on exports to the United States despite the much-trumpeted deal sealed by President Donald Trump and Prime Minister Sir Keir Starmer.

Downing Street said at the time of the announcement last week that these would be slashed immediately, reducing car tariffs to 10 per cent, and steel and aluminium to zero.

And the UK aerospace sector also looked set to gain, with US commerce secretary Howard Lutnick saying that engines from Rolls-Royce and other aeroplane parts could be imported tariff-free.

But the deal has yet to take effect. An aerospace industry source said: ‘It’s increasingly causing issues. 

'We’re still waiting for that clarity, and it’s incredibly frustrating and disheartening that it’s not here.’

A Government spokesman said: ‘We need to implement the deal in a way that works for British businesses and close engagement will be our top priority in the weeks ahead.’

The admission that the process will take weeks came as Chancellor Rachel Reeves boasted that two trade deals agreed – with the US and India – showed ‘our plan for change is working’ though she admitted the Government was still ‘working through the detail’ on the US arrangement.

It is an embarrassment after the Government boasted that it had saved thousands of jobs as a result of the deal, which is the first such accord between Trump and any other country.

In particular, Jaguar Land Rover was said to have been lining up job cuts before the announcement was made – though it has since denied action was in the offing.

Adrian Mardell, its chief executive, said this week that he was still waiting for an update on timing – comments echoed by the boss of rival Bentley.

Meanwhile, industry body UK Steel said that it has not yet ‘been given a clear timeline on when the tariffs will be reduced’ and firms ‘still face the same 25 per cent tariff with no idea when it will change’. 

It is a huge setback for a beleaguered industry which has suffered thousands of recent job losses.

Tory business spokesman Andrew Griffith said: ‘More than a week ago the Government hailed the partial reversal in tariffs saying firms were days away from lay-offs. But since their rushed announcement, no details or timings have emerged.

‘Rather than lead us up a garden path, the Government must immediately publish the details of the deal and when the benefit will start.’

David Henig, a former UK trade negotiator, told the Financial Times: ‘The problem with doing a quick trade ‘deal’ like this is that nobody knows when or how it is to be implemented, which leaves business winners and losers wondering what is going on and, indeed, whether it will happen at all.’