The Northern Ireland Office has been unable to say whether it will fly the Union flag from its new headquarters in Belfast city centre.
Secretary of State Brandon Lewis' department is relocating from the Stormont estate to Erskine House at the corner of Arthur Street and Chichester Street, joining officials from other UK departments.
The government changed its guidelines last year to now encourage departments to fly the Union flag all year round rather than only on designated days.
In Northern Ireland some government buildings are legally restricted to flying the flag on designated days, but Erskine House is not bound by these regulations.
The NIO was asked whether the Union flag would be flown from the eight-storey building all year round, on designated days, or not at all.
The department did not provide a clear response.
In a statement an NIO spokesman would only say, "Erskine House is not designated for the purposes of the Flags Regulations in Northern Ireland."
It is understood the NIO is looking at the "feasibility" of flag-flying at Erskine House, but it remains unclear whether the Union flag will be flown from the building.
TUV East Antrim candidate Norman Boyd said the NIO should follow the UK government guidance introduced last year.
He added: "When the policy was introduced, the government said it would be 'a proud reminder of our history and the ties that bind us'. That being so, the flag should be flown in all parts of our nation, including Northern Ireland.
"Yet in this response the NIO leaves open the possibility of the Union flag not flying from their new headquarters in Northern Ireland at all.
"Such a move is grossly insulting to the people of this part of the UK who are and remain British because that is the wish of the people of Northern Ireland.
"The NIO need to come clean on this issue and state clearly that the Union flag will fly year round from its new HQ."
The NIO move will bring together under one roof officials from different UK government departments including HMRC and the Competitions and Marketing Authority.
At its former headquarters at Stormont House, the NIO displayed the Union flag on designated days.
It said last year it was drafting its own "flag-flying policy" after the new UK government guidance was introduced.
Flags and emblems remain contentious in Northern Ireland's divided communities.
In 2012 a decision by Belfast City Council to reduce the number of days on which the Union flag is flown from City Hall sparked widespread protests and disorder.
A long-delayed Stormont report aimed at addressing cultural disputes was published last year but was unable to reach consensus on many issues over flags.
