The National Trust has removed a large Union flag that was found attached overnight to the Penshaw Monument, saying it had been placed on the Grade I-listed structure without permission and that staff will assess whether any damage was caused.

The flag was discovered attached high on the 70-foot monument on Friday. The Trust, which has owned the site since 1939, said anything fixed to historic buildings or structures will be taken down and that routine checks will follow to determine whether the stonework or fixtures were harmed.

Built between 1833 and 1845 in memory of the 1st Earl of Durham, Penshaw Monument is a replica of a Greek temple and is one of the North East’s most recognisable landmarks. The National Trust described the monument as "an important part of our shared local and national heritage" and said in a statement: "A flag which has been attached to the Grade I listed Penshaw Monument will be removed, as will anything that's attached to historic buildings without permission. We will assess whether any damage has been caused to the monument."

The incident at Penshaw is the latest in a wave of unauthorised flag displays reported across England in recent weeks. Campaigners have fastened Union Jacks and St George’s Crosses to lampposts, road signs and landmarks, prompting some local authorities to remove banners on health and safety grounds and urging the public not to tamper with street furniture.

Earlier this week the Westbury White Horse, a chalk hill figure in Wiltshire carved more than three centuries ago, was altered with two lengths of red fabric pinned to it. English Heritage, which cares for the site, said it would remove the material as soon as possible; Wiltshire Police said it was not investigating the incident. A local resident, Velisa Russell, who walks past the hill regularly, was quoted as saying: "Luckily there's no damage as red material was used. It's more an act of patriotism, not vandalism. Just a bit of fun."

The displays have been tied to a grassroots campaign variously described as Operation Flying the Colours or Operation Raise the Colours, which organisers say grew out of protests over asylum hotels and recent demonstrations in Birmingham in solidarity with Gaza. Supporters say the actions express national pride; critics warn the movement has been co-opted by far-right activists.

Several Conservative politicians have publicly supported flag-flying. Shadow Justice Secretary Robert Jenrick was among those who went out to hang flags, and Tory leadership hopeful Kemi Badenoch wrote in a national newspaper that flags were being flown as "symbols of unity, nationhood and optimism," adding that "there is nothing racist about flying the flag of your nation." Other councils, including Tower Hamlets and Birmingham, have removed unauthorised displays or warned they would do so.

Some of the campaign's organisers and backers have controversial associations. Operation Raise the Colours was co-founded by Andrew Currien, also known as Andy Saxon, who has been described as an ally of Stephen Yaxley-Lennon, also known as Tommy Robinson, an activist linked to the English Defence League and Britain First. Campaign organisers have reportedly accepted donations of flags from Britain First; the organisation has repeatedly denied accusations that it is far-right or fascist.

Heritage bodies and local authorities have urged restraint, saying that attaching items to listed buildings or protected landscapes risks physical damage as well as legal consequences. The National Trust and other custodians of historic sites say they will continue to remove unauthorised fixtures and pursue assessments and repairs where necessary.

The Penshaw Monument removal underscores a broader debate over public displays of national symbols and how they intersect with the protection of historic sites. Authorities and heritage organisations continue to monitor incidents and stress that any future adornments should be carried out only with proper permission and safeguards in place.