The original post featured an Irish flag emoji in the caption10 Downing Street - Instagram
Ulster Unionist Party leader Doug Beattie said it showed Westminster did not “understand us or know us”.
He used the incident as a vehicle for calling for power-sharing in Northern Ireland.
“We are better served with devolved Government,” he said.
“There are people out there who want to hand all the devolved power we have back to Westminster and here is what Westminster is doing,” he told the Nolan Show.
“They don't understand Northern Ireland.”
Northern Ireland has been without a devolved government at Stormont since February 2022
Despite the hasty edit, people across social media were quick to notice the mistake.
One said: “Did anyone in No10 flag the error?”
Another joked: “Thanks for flagging that up.”
A third chimed in: “That can’t be real can it?”
Northern Ireland has been without a devolved Government at Stormont since February 2022 after the DUP refused to assent to the election of a speaker as part of a protest against the Northern Ireland Protocol.