Labour could ditch plans for a customs union with the EU if Brussels refuses to give the UK a say in making new trade deals, Jeremy Corbyn has said.

The Labour leader’s spokesman insisted plans to stay in the customs union after Brexit were “not a commitment” after Mr Corbyn used a major speech to say his party would seek to negotiate a deal to maintain existing trading terms.

Instead, Labour would leave open the option of walking away from negotiations if EU leaders make clear the UK could only be part of the tariff union if it accepts it will not have a say over deals that are made.

It means a Labour government could ultimately adopt a similar position to the Conservatives and rule out any customs union with the EU – a move that would likely see tariffs imposed on goods and lead to a hard border in Northern Ireland.

Some Labour MPs said their leader’s shift towards staying in a customs union was “nowhere near enough”.

Mr Corbyn used a keynote speech at the National Transport Design Centre in Coventry to announce Labour’s intention of remaining in a trading bloc.

“Labour would seek to negotiate a new comprehensive UK-EU customs union to ensure that there are no tariffs with Europe and to help avoid any need for a hard border in Northern Ireland,” he said.

However, he added: “We are also clear that the option of a new UK customs union with the EU would need to ensure the UK has a say in future trade deals.

“A new customs arrangement would depend on Britain being able to negotiate agreement of new trade deals in our national interest.

“Labour would not countenance a deal that left Britain as a passive recipient of rules decided elsewhere by others. That would mean ending up as mere rule takers.”

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Mr Corbyn’s aides later confirmed that a potential new customs union with the EU is merely “an option” and “not a commitment”, leaving open the option of a Labour government walking away from a deal if the EU does not meet demands for a seat at the negotiating table.

His spokesman told The Independent: “We’re saying a customs union between the UK and the European Union is an option – we’re not saying that’s a commitment.

“It’s an option and we would seek to negotiate that option.

“It’s part of a whole package of different approaches to different issues. If you can’t negotiate some parts of the package then obviously you have to have alternative options.”

He said Labour would not support a Brexit deal that would “damage jobs and living standards”, but declined to say that the lack of a customs union in any deal the Government negotiates with Brussels would result in the party opposing against the package when Parliament is giving a “meaningful vote” on the issue.

Some Labour MPs demanded Mr Corbyn go further and also pledge to keep the UK in the EU single market.

Chris Leslie, a supporter of the pro-EU Open Britain campaign, said: “Jeremy Corbyn’s speech is not the end of Labour’s debate on Europe.

“His commitment to the customs union is welcome but it is nowhere near enough.

“Staying in the single market is absolutely essential if we are to protect manufacturing jobs and investment and to avoid a hard border in Ireland.