Britain cannot accept Northern Ireland being in a separate customs territory from the rest of the UK, Prime Minister Theresa May’s spokesman said on Tuesday. Brexit talks have stalled over a disagreement on the Northern Irish backstop, an insurance policy to ensure there will be no return to a hard border on the island of Ireland if a future trading relationship is not agreed in time. The EU could look to “anchor” a reference in the legally binding Withdrawal Agreement to Britain’s proposal to keep the whole of the UK in a customs partnership with the EU, Reuters said. The spokesman was asked whether Britain would be prepared to accept the Northern Ireland backstop if there was a link to a future treaty agreement on a UK-wide arrangement. “Any circumstance in which Northern Ireland could be in a separate customs territory to the UK is unacceptable,” the spokesman said.