The US trade deal will be implemented "within a very short time", the Prime Minister has said after Donald Trump exempted Britain from a hike in steel tariffs.
Sir Keir Starmer suggested to the House of Commons on Wednesday that the deal struck last month could come into effect "in just a couple of weeks".
Once implemented, the agreement would effectively eliminate tariffs on British steel and aluminium exports to the US.
We are the only country in the world that isn't paying the 50% tax on steel and that will be coming down. We are working on it to bring it down to zero, that is going to happen
Those tariffs currently stand at 25% after Mr Trump said he would "provide different treatment" for the UK while he increased the levy to 50% for the rest of the world.
But the situation could still change again in July, when the US is set to either increase the tariffs to 50% or introduce the quotas in the US-UK agreement, effectively eradicating the tax, depending on whether the deal is implemented.
Challenged over the uncertainty during Prime Minister's Questions by Conservative leader Kemi Badenoch, Sir Keir said: "We are the only country in the world that isn't paying the 50% tax on steel and that will be coming down.
Sir Keir Starmer said he expected the trade deal with the US to be implemented 'within a very short time´ during Prime Minister´s Questions on Wednesday (Alberto Pezzali/PA)
"We are working on it to bring it down to zero, that is going to happen."
Responding to further questions from Liberal Democrat leader Sir Ed Davey, Sir Keir told MPs: "We have a deal and we are implementing it and within a very short time I am confident we will get those tariffs down in accordance with the deal."
Adding that he expected MPs would be "very pleased at the outcome of that", he said: "Let's come back in just a couple of weeks when we have implemented it."
After Prime Minister's Questions, Downing Street said Sir Keir's confidence in finalising the deal was due to "constant dialogue" with the US.
But the Prime Minister's official spokesman would not guarantee that the deal would be in place by the July 9 deadline set by Mr Trump, telling reporters: "Obviously our aim is to implement this deal as quickly as possible and you have just heard from the PM in the House that we are hoping to provide an update on that in weeks."
Earlier on Wednesday, Transport Secretary Heidi Alexander told the BBC the Government would bring forward the legislation needed to implement the deal.
Meanwhile, both the steel industry and trade unions have urged the Government to finalise the agreement with Washington.
It is time for the Government to admit that Trump's White House is not a reliable ally and get tough on ending this trade war by backing British businesses
Gareth Stace, head of the industry body UK Steel, said Mr Trump's decision to keep tariffs on British steel at 25% was a "welcome pause" but warned that continuing uncertainty was making US customers "dubious over whether they should even risk making UK orders".
Alasdair McDiarmid, assistant general secretary of the Community union, also welcomed the "reprieve" from the 50% rate, and added it was "vital that the UK locks down the US trade deal to avoid punitive steel tariffs going forward."
But the Lib Dems urged Sir Keir to stand up to Mr Trump, saying the president had changed the terms of a deal he had already signed.
Following Prime Minister's Questions, Sir Ed called on the Government to support his party's "Buy British" campaign, saying: "Donald Trump has taken our lunch money and is now coming back for more.
"Any deal he signs is already through the Oval Office shredder.
"It is time for the Government to admit that Trump's White House is not a reliable ally and get tough on ending this trade war by backing British businesses."
The Conservatives have said that Labour's "botched negotiations have left businesses in limbo".
Shadow business and trade secretary Andrew Griffith said: "Keir Starmer stood in front of the nation and insisted to the British public that his Labour Government had achieved a trade deal with the US - and now one month later our industries face a fresh tariffs blow.
"So once again it seems that Keir Starmer's promise was just like the rest: hollow and broken. Labour's botched negotiations have left businesses in limbo and this country simply cannot afford their continuing failure."