Demands by a leading British minister to quit the EU's customs union will make it "extremely difficult" to maintain an open Border with Northern Ireland, Minister for Foreign Affairs Charlie Flanagan has said.

Saying he was “surprised” by international trade secretary Liam Fox’s declaration, Mr Flanagan cautioned: “I’m not sure that is widely shared among his colleagues.”

In a speech, the Conservative minister suggested that the UK would leave the customs union and negotiate its own trade deals as an independent member of the World Trade Organisation.

Speaking to members of the British-Irish Chamber of Commerce, Mr Flanagan said such an outcome would be “of specific concern to us” because it would make “an invisible Border extremely difficult”.

The EU’s customs union, which includes all EU members and others, including Turkey, allows the tariff-free movement of goods within it and imposes a common tariff on goods entering from the outside. The EU negotiates trade agreements for the customs union as a whole.

In a speech in Manchester on Wednesday, Mr Fox voiced strong support for a fully independent UK place at the WTO table.

Britain would be free to strike its own trade deals, but it would mean leaving the customs union unless it negotiates continued access to the EU single market.

Hard lobby

Despite Mr Flanagan’s belief that Mr Fox’s position will not be supported, his comments suggest that the lobby for a “hard Brexit” – a complete departure from the EU’s single market – is gaining strength in London.

Enterprise Ireland chief executive Julie Sinnamon, who spoke at the event in Iveagh House, said that companies should immediately take steps – such as hedging currency risks – to prepare for the eventual departure of the UK.