Bidston Observatory on Wirral 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 Observatory, which towers above Wirral from its Bidston Hill base.

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 Two.

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

Last year Wirral council passed 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 site 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 was listed for sale through estate agents Brennan Ayre O’neill and has sparked “reasonable” interest according to owner 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.”

While no offers have been made on the site, Mr O’Neill added that was typical for sales of this kind, with most bids expected to come in on the deadline day.

He added that 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 of the observatory, fearing the impact development would have on the site and popular walking trail on Bidston Hill.

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.

He wrote: “We, the Friends of Bidston Hill, supported the application for listed buildings consent. We did so because the plans were sympathetic to the environment of Bidston Hill and the heritage of the building, because they provided a common area for heritage displays, and most importantly, because a residential use would be a better outcome than the status quo – unwanted, slowly deteriorating, office space.

“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.”