UK cultural landmarks such as Stonehenge could be stripped of their coveted world heritage status unless the government curbs “ill-advised development” and protects historic sites for future generations, a Unesco chief has warned. Dr Mechtild Rössler, the director of Unesco’s World Heritage Centre, urged ministers to “do everything” they could to conserve the UK’s treasures after Liverpool became only the third place in nearly 50 years to lose its revered title. Rössler said developers should be made more aware of the international value of places such as Stonehenge before proposing potentially harmful projects. She said: “These are the most outstanding places we have on Earth. If we are not capable of protecting these, for me the question is what will be left on this planet?” The intervention came before Thursday’s high court ruling that the transport secretary, Grant Shapps, had acted unlawfully in granting permission for a two-mile tunnel to be be built at Stonehenge. However, the government has the chance to appeal against the ruling and, if the project does get the go-ahead, the Wiltshire stone circle is expected to be placed on Unesco’s “in danger” list – a precursor to being stripped of world heritage status – in another humiliating blow for Britain. Rössler, a world-renowned expert in cultural heritage and the history of planning, said the UK government “should take into account the beneficial provisions of the world heritage convention and do everything to protect this heritage for generations to come because we are not protecting this heritage for us today”. She added: “We need to ensure that the generations to come benefit from the same heritage we can benefit from today.” Heritage bodies have warned that the UK risks losing its reputation for conserving historic sites because controversial developments, such as the Stonehenge tunnel and Everton’s new football stadium, have been allowed to go ahead by the government in recent years. Rössler said she was surprised that Shapps had agreed to the £1.7bn Stonehenge tunnel despite the government’s planning inspectorate concluding it would cause “permanent, irreversible harm” to the world heritage site. Stonehenge is “one of the most emblematic sites we have on the World Heritage list”, she said, adding that it would have been “much better” if the government had discussed the development further with Unesco before granting approval in November 2020. She said the government must produce a heritage impact report by February “with a view of [Unesco] putting Stonehenge on the list of world heritage in danger”. “I really encourage the authorities of the UK to get everybody together and to see what the best solution would be because the warning was made several times,” she added. The stone circle, which attracts nearly a million tourists a year, has been on the world heritage list since 1986. It would be the best-known cultural attraction to be delisted if such a step were taken, giving the UK the ignominious distinction of being the first country to have two historic sites removed from the prestigious list. Britain’s plethora of historic monuments, which range from prehistoric sites such as Stonehenge to medieval castles and Roman forts, contribute billions of pounds to the economy each year and draw in millions of visitors from around the world. Rössler, who has led Unesco’s World Heritage Centre for six years, said the decision to strip Liverpool of its title was “a loss for all of us” but that the city’s leaders had failed to address its concerns for years about the Liverpool Waters project by Peel Holdings, the major developer owned by the reclusive billionaire John Whittaker. “The warning was in 2012,” she said. “There was no feedback in terms of complying with the request from the world heritage committee to stop the situation which leads to the loss of outstanding universal value. That is the problem.” Asked whether Unesco was concerned about the UK’s management of its historic landmarks, she said: “The UK has all the policies in place, you have the institutional bodies … and management plans for most of the sites in place. “However, I have to say sometimes there is ill-advised development. What I would like to see for the future of world heritage [is] that everybody is in the same boat. “That includes developers to be better aware of what the values of the sites are so that projects don’t threaten the OUV [outstanding universal value] of these places. That is a challenge we have everywhere and we have it also in the UK.” Rössler called for more financial support for the UK’s world heritage sites, which on average receive only about £1m a year from central government and often rely on volunteers. Unlike other countries, the UK has not established a national foundation to fund these treasured sites, as it has been encouraged to do under the Unesco world heritage convention. She added: “I think there needs to be more support for world heritage but in which way authorities are doing that is really left to the national authorities and to the local authorities.” A government spokesperson said: “The UK is a world leader in cultural heritage protection with 33 Unesco world heritage status sites on the list, including the slate landscape of north-west Wales, which was added this week. “We welcome the confirmation that the world heritage committee does not recommend that Stonehenge be added to the list of world heritage in danger this year. “Protecting the heritage and archaeology of the Stonehenge site is a priority and we will continue to work closely with Unesco, Icomos [the International Council on Monuments and Sites] and the heritage and scientific community on next steps.”