A proposed meeting between King Charles and the president of the EU Commission just days before an expected deal on the Northern Ireland protocol has been cancelled at the last minute.
Sources close to the palace said this was done for 'operational reasons' but the meeting was seen by some as an attempt by the government to politicise the monarchy.
King Charles had been due to meet Ursula von der Leyen on Saturday, but the event was cancelled at the eleventh hour.
Former cabinet minister Jacob Rees-Mogg told the Independent: “(The government) would not normally call upon the sovereign to advance a particular policy aim that is controversial within British politics. So I think it's very much on the borderline of constitutional propriety.”
DUP peer Nigel Dodds tweeted: “To plan for politicising the Monarchy in this way is very serious and reinforces the questions about No 10’s political judgment over the Protocol.”
It is understood that King Charles would not have been involved in any direct negotiation. “His involvement would only have been at the government’s request and he would have had no part in the negotiations whatsoever. It is not going to happen due to operational reasons,” a source said. “Any suspicion of any other motive would be misguided.”
The Prime Minister and Ms von der Leyen are expected to hold talks on the Protocol this weekend, with an agreement seen as likely within days.
But any deal could trigger a clash with Conservative Brexiteer hardliners and the DUP, who have warned their tests must be met before they can accept a new settlement and re-enter power sharing in Northern Ireland.
Northern Ireland’s largest unionist party rejects the current deal, which it warns puts a border down the Irish Sea.
Sky News first reported the planned meeting.
Politicising the monarchy is seen as a constitutional taboo.
But the monarch has occasionally intervened in politics. In 2014 the then Queen let it be known that she did not want Scotland to leave the UK in the run up to the independence referendum.
Labour's shadow Northern Ireland secretary Peter Kyle said: "Sunak is already showing that negotiation is better than fighting but his lack of political acumen and judgement is once again undermining his chance of success."