Sir Keir also reiterated his support for the Prime Minister’s decision to blame Russia for the nerve agent attack in Salisbury
He added: “This was a chemical attack in our country. The Prime Minister set out her reasons for pointing the finger at Russia; she’s been joined by the US and France and Germany. Russia has to put up an explanation.”
Sir Keir made the comments as he visited Leeds to present the Fastest 50 awards, which honour the fastest growing companies in the region.
Labour has said it would support remaining in a customs union with the European Union after Brexit.
Speaking before he addressed the awards, Sir Keir told The Yorkshire Post: “The thing that has really struck us is the need to make sure that manufacturing can survive and thrive in the UK. Because of the supply chains, that can only really happen if you’ve got a customs union.
“Now, we’re obviously not against new trade deals with other countries; that’s a very good thing, but it shouldn’t be at the expense of our trade with Europe and we think, frankly, that if we were to pool our resources with the EU we would get better trade deals in the future anyway.
“It makes real sense to go for a customs union. What was striking about the position that we adopted is that not only did it get the backing of the Labour Party and the trade unions, but quite a lot of business organisations came out in support of it. There was a general sense that this was a sensible proposition on the table that is actually going to work for businesses.”
He said steps must be taken to avoid the return of a hard border in Northern Ireland after Brexit.
He added: “This isn’t a technical question of how do you get people over a border or goods over a border. The two communities in Northern Ireland bravely came together in peace 20 years ago and not having a border is a symbol; it means something in the hearts of people in Ireland and in Northern Ireland and so that is a solemn commitment that has to be kept to.
“What I would say to the Government is, ‘How on earth are you going to achieve that, if you won’t contemplate a customs union with the EU, because I have not met anybody credible who suggests you can achieve the ambition of no border in Northern Ireland without a customs union.”
Sir Keir also warned that the UK must “not to get carried away with models that have worked for other countries or islands”.
He added: “I think the Prime Minister is right to say it’s got to be a UK- EU agreement.
“I disagree with her about what should be in that agreement; but it’s got to be something that works for the UK and I think trying to take bits of models that may have worked in other areas is the wrong approach .
“So we need to set out what we’re trying to achieve and hard-wire that into an agreement with the EU.”
Sir Keir gave his unqualified support to Mrs May’s approach to tackling the nerve agent attack in Salisbury when he appeared on BBC1’s Question Time on Thursday night.
He told The Yorkshire Post: “It’s very important that we call out the dreadful incident in Salisbury. It shocked everybody because everybody in their village, their town and their city thinks, ‘That could have been my city, town or village.
“What the Prime Minister has done is right and we now have to wait and see. The criminal investigation needs to be thoroughly carried out and that needs space. But it is really important that we stand together in calling out this appalling act.”
Labour leader Jeremy Corbyn, whose response to the attack has led to criticism from some on his backbenches, said “the evidence points towards Russia” being responsible - but the possibility of gangsters being behind the attack rather than the Kremlin could not be excluded.
He warned Mrs May not to “rush way ahead of the evidence” - highlighting the way international crises such as the Iraq War had seen “clear thinking” overwhelmed by “emotion and hasty judgments”.
Sir Keir said: “What Jeremy has said, loud and clear, is that this is an appalling act, that accountability must lie with Russia and he’s been fully supportive of the Prime Minister’s action. I think that has got lost in this somewhere.
“The whole of the Labour movement is united in condemning what has happened and supporting the response.
“Obviously, there has got to be a criminal investigation. We think there should be further action looking at the money that’s flowing around in this country.
“The Russian oligarch money has been a problem for a very long time. But, one step at a time, is the right thing to take action against Russia at the moment.”
Mr Putin’s spokesman said today: “We have said on different levels and occasions that Russia has nothing to do with this story.”
The Fastest 50 awards, which are run by The Yorkshire Post with the law firm Ward Hadaway, honour the fastest growing firms in the region.
The winner of the fastest growing small business trophy at this year’s awards was Azzure IT, and Production Park secured the prize for the fastest growing medium-sized business. The winner of the award for fastest growing large business - and the overall fastest growing business - was Pure Retirement.
The event, which also included a speech from Greg Wright, The Yorkshire Post’s deputy business editor, was held at Aspire in Leeds.
A special supplement to celebrate the awards will be published with The Yorkshire Post on Tuesday.