A sign for Customs and Excise is seen on a road near Kileen, Northern Ireland, October 17, 2018. REUTERS/Clodagh Kilcoyne

LONDON (Reuters) - It would be unacceptable for Northern Ireland to be in a separate customs territory from the rest of the United Kingdom after Brexit, British Prime Minister Theresa May’s spokeswoman said on Friday.

The Financial Times reported on Thursday that the European Union had floated a tentative plan which would see Northern Ireland remain in a deep customs union with the bloc while the UK would be in a more “bare bones” customs arrangement.

“We have put forward our proposals and the EU is engaging with us but negotiations continue,” the spokeswoman said when asked about the report.

“It would be unacceptable for Northern Ireland to be in a separate customs territory to the rest of the UK.”