The DUP has called for an equality investigation into a decision to prevent a tree being planted on the Stormont estate to mark the Queen’s platinum jubilee.

The party has accused Sinn Fein Finance Minister Conor Murphy of “intolerance and disrespect” after he declined approval for the tree planting.

The DUP has written to the Equality Commission for Northern Ireland, which oversees adherence to equality laws in the region, asking for the decision to be investigated.

Mr Murphy, whose department has responsibility for the grounds of the Stormont estate, insisted that official policy dictated that only “international events” could be commemorated with physical structures or planting.

DUP Assembly member Joanne Bunting had sought permission to plant a tree on the estate as part of the Queen’s Green Canopy project, an initiative that encourages people across the UK to “Plant a Tree for the Jubilee”.

In a written reply to East Belfast MLA Ms Bunting, seen by the PA news agency, Mr Murphy outlined the rationale for declining approval.

“The Department of Finance receives occasional requests for memorials on the Stormont estate for various causes,” he wrote.

“I trust you will appreciate the need to balance the duty to appropriately manage the estate with the desire of people and organisations to provide lasting tributes to commemorate events.

“Since 2016 my department’s policy on commemorative structures or planting on the grounds of the Stormont estate is to approve only those requests which commemorate international events such as World Aids Day, International Labour Day or Holocaust Memorial Day. This extends to the installation of plaques, benches or similar structures.

“I therefore cannot give approval for a tree to be planted on the estate but I wish you well in marking this event.”

The rejection is the latest in a series of recent incidents where unionists have accused Sinn Fein of preventing commemorative acts associated with their tradition.

Last year, Sinn Fein vetoed a proposal put to the Assembly Commission to place a commemorative stone in Stormont’s Parliament Buildings to mark Northern Ireland’s centenary.

The commission, made up of representatives of the main parties, has responsibility for Parliament Buildings, whereas the Department of Finance is responsible for the surrounding grounds.

Sinn Fein insisted the stone had been “designed and commissioned by representatives of one tradition” and accused unionists of failing to consult with other parties about their plan.

Last year, Mr Murphy also turned down a DUP request to plant a commemorative rose bush to mark Northern Ireland’s centenary within the Stormont estate.

Away from Stormont, there was a similar row at Belfast City Council in October when Sinn Fein blocked a proposal to light up City Hall to mark the centenary.

At the time, Sinn Fein party group leader on the council Ciaran Beattie said the partition of Ireland was “nothing to celebrate” and argued the symbolic lighting of the building would have adversely impacted nationalists in the city.

Ms Bunting has criticised the rejection of her tree proposal and called on the Equality Commission to step in.

The DUP has pointed out that former DUP finance minister Sammy Wilson gave permission for a tree to be planted at Stormont to mark the 125th anniversary of the GAA in 2009.

“This is further proof that Sinn Fein doesn’t want a unionist about the place,” said Ms Bunting.

“They demand tolerance and respect but demonstrate nothing other than sheer intolerance to mark Northern Ireland’s very existence.

“They denied the planting of a rose bush, the lighting of the building and a commemorative stone for the centenary.

“Now we have yet another display of blatant intolerance and disrespect with a refusal to mark Her Majesty The Queen being the longest serving monarch in history of the world.

“The Equality Commission must look at this matter. Whilst Conor Murphy has responsibility for the Stormont estate, the grounds belong to the people, not Sinn Fein’s anti-unionist mind set.

“He has got carried away with control and Connolly House (Sinn Fein HQ in Belfast) is overstepping the mark. This is just basic bad manners.

“Unionists will remember this intolerance at the polls. Votes will not be wasted.

“When such narrow mindedness is on display by Sinn Fein with their current mandate, we need more unionist MLAs returned to Stormont to put a marker down that people who believe in Northern Ireland should not and will not be treated in this way.”