FILE PHOTO: DUP deputy leader Nigel Dodds speaks during the party's annual conference in Belfast, Northern Ireland, November 25, 2017. REUTERS/Andrew Paton

DUBLIN (Reuters) - A new EU proposal to operate checks on goods along the Britain-Northern Ireland sea route will still mean an unacceptable border between the two, the deputy leader of the Northern Irish party backing Britain’s minority government said on Wednesday.

The European Union’s chief Brexit negotiator Michel Barnier said on Tuesday the bloc was ready to improve its proposal for an “insurance policy” backstop arrangement on how to manage its Irish border that would avoid creating a physical customs border on the Irish Sea.

British Prime Minister Theresa May rejected the previous EU proposal on how to avoid a “hard border” on the United Kingdom’s only land border with the EU, saying it would effectively slice Northern Ireland away from mainland Britain, a position staunchly backed by her pro-British allies in Belfast.

After May lost her party its majority in parliament in a snap election last year, she is dependent on the Democratic Unionist Party’s (DUP) 10 lawmakers in the 650-seat British parliament to ensure she can pass legislation.

“So Michel Barnier says he can do different kinds of checks between Northern Ireland and the rest of the UK as if that makes it more palatable. The fundamental point is that internal U.K. checks are only needed if it is intended to separate Northern Ireland from Great Britain,” DUP Deputy Leader Nigel Dodds said in a statement.

“Despite the talk of ‘improvements’ the backstop being insisted upon by the EU ... still means a border down the Irish Sea although with different kinds of checks. The fact is that both Theresa May and the Labour Party have said no British prime minister could accept such a concept.”

With just over six months to go before Britain leaves the EU, reaching agreement on a backstop arrangement for the border between Northern Ireland and EU-member Ireland remains the thorniest issue in negotiations.