An historic Merseyside landmark could be sold for development into flats within days.

Developers have been given a deadline of November 30 to make offers on Grade II-listed Bidston Observatory, which  towers above Wirral from Bidston Hill.

But campaigners  – concerned about the potential consequences of development – have called for a delay to the sale.

Built in 1866, Bidston Observatory has had several uses, including predicting the tides for the D-Day landings in World War II.

Abandoned in 2000 the observatory, owned by the Natural Environment Research Council (NERC), is visible from north Wales and Liverpool.

Last year Wirral council gave planning permission to convert the two-storey building – which also has a two-level basement – into four flats.

Now, an advertisement for the 14,500 sq ft site on property listings website Rightmove invites “Best and final offers by the 30/11/13 please for the former Bidston Observatory with planning permission for conversion to four apartments: comprising a substantial building with associated land located on the ridge of Bidston Hill and Park Wood.”

The site, which has been the subject of sale attempts in the past, is listed for sale through estate agents Brennan Ayre O’Neill (correct with lower case n) and has sparked “reasonable” interest according to partner Rob O’Neill.

Mr O’Neill said: “It’s very unusual and for that we are thrilled to be invited to sell such an unusual landmark.”

He hoped a “sensitive, compassionate” buyer could be found for the historic site.

But campaigners from community group Friends of Bidston Hill have expressed disappointment at the planned sale, fearing the impact development would have.

In a post on the group’s website, chair Rob Caligari called for the sale to be delayed, claiming opportunities for a “community use” for the site had not been explored.

Mr Caligari said “residential use would be a better outcome than the status quo – unwanted, slowly deteriorating, office space” but wrote:  “We would support a community use even more whole-heartedly… 120 years ago, the Bidston Hill Committee campaigned to secure the land on Bidston Hill for the public.

“After many years and many setbacks they succeeded. They prevented the building of 400 dwellings along Vyner Road, and raised the money to buy some 46 acres of land on Bidston Hill.

“The parkland on Bidston Hill that we all enjoy today is thanks to their untiring efforts.

“We need the Bidston Hill Committee to be re-born today. Their work is not quite finished. But we need time.”