Liverpool could lose favour if it messes with the Three Graces

For a century, mariners sailing into the Mersey port have been greeted by the majestic Three Graces. The Royal Liver Building and its less famous sisters, the Cunard and Port of Liverpool buildings, have dominated the skyline and earned the waterfront international recognition in the form of Unesco World Heritage Site status, along with the Acropolis, the Pyramids, Cambodia's Angkor Wat temple, the Taj Mahal, Stonehenge and the Great Barrier Reef.

This Tuesday, however, that looks set to come to an end. The city is expected to approve the UK's biggest planning application: a £5.5bn development that will relegate the Three Graces to bit-players in a landscape dwarfed by skyscrapers.

The development will threaten the city's World Heritage status, putting it in line to become only the third place ever deleted from Unesco's list.

The planning decision is so controversial that, if passed, it will be subject to a legal challenge and referred to the Communities minister Eric Pickles.

Unesco has concluded in a report that the development would "irreversibly damage" the site, and "relegate The Three Graces to playing second violin".

Planning officials recommend that the council approves the project which is expected to create 20,000 jobs. Their report says that Unesco will add Liverpool to the "World Heritage in Danger" list, before deleting it from the main World Heritage list "if/when the 'damaging' components of the proposal are commenced".

English Heritage has formally objected, meaning that the development, if approved, will automatically be referred to Mr Pickles. Henry Owen-John, its regional director, said: "It is possible to have a scheme that delivers jobs and growth, without causing so much harm to the city's heritage."

The Victorian Society also objected, writing: "Dock walls and historical buildings would be completely overshadowed, literally and metaphorically."

Peel Holdings, behind the Liverpool Waters development, uses the cultural status to attract property buyers, promoting the "stunning Unesco-listed waterfront" in advertisements. Tourism brings in £3bn annually, with 42,000 jobs depending on it, according to the Mersey Partnership.

The Liverpool Preservation Trust, which launched an e-petition yesterday asking for the Department for Culture to scrutinise the application, is consulting barristers. Its founder Wayne Colquhoun, who hopes to mount a legal challenge, said: "Liverpool, a past European capital of culture, should be able to develop while protecting cultural assets, rather than turning it into Trafford Park-on-Mersey."

Peel Holdings, chaired by the billionaire Mark Whittaker, declined to comment on the development which includes 9,000 apartments, hundreds of offices and a cruise terminal.

Liverpool Council's chief executive, Ged Fitzgerald, confirmed the planning committee would make its decision this Tuesday.

Liverpool was awarded World Heritage Site status in 2004. If it loses that designation it will join a very short deleted list alongside Oman's Arabian Oryx Sanctuary, where prospecting for oil and poaching depleted the rare birds, and the Dresden Elbe Valley, which lost its status in 2009 after plans for the Waldschlösschen bridge were approved.