International Trade Secretary Liam Fox has said that Britain cannot be involved in any customs union with the EU following Brexit.
The minister's comments came as Theresa May insisted that it was not necessary to choose between the alternatives of frictionless trade with Europe and the ability to strike new deals elsewhere in the world.
The Prime Minister appeared to leave the door open to some form of customs agreement when pressed on the issue during her visit to China.
She was asked on Sky News whether the £9 billion of deals struck during the three-day trip showed it was possible to stay closely aligned with the EU and its customs union while still increasing trade with countries like China.
She responded: "What I want to do is ensure that we have got the best possible trade arrangements with China and with other countries around the world once we have left the European Union. I do want to do those free trade agreements."
Downing Street has rejected a report in The Financial Times that ministers are privately considering a customs union arrangement for post-Brexit trade in goods in order to avoid disruption to exports.
Fox indicated that the UK was also ruling out entering into any other customs union arrangement with the remaining EU27.
He told Bloomberg TV in Shanghai: "It is very difficult to see how being in a customs union is compatible with having an independent trade policy because we would therefore be dependent on what the EU negotiated in terms of its trading policies, and we'd be following behind that.
"We have to be outside of that to take advantage of those growing markets. One of the reasons we are leaving the European Union is to take control, and that's not possible with a common external tariff."
May has repeatedly said that Brexit will mean leaving the existing EU single market and customs union arrangements.
The customs union currently frees members from tariffs when trading with one another but requires them to observe a common external tariff regime and not to strike deals with third countries.