A £12.5million development has been put on hold over fears an underground sink hole could cause a seafront cliff to collapse.

Redab Properties wants to knock down the 100-year-old Esplanade Pub, in Western Esplanade, and replace it with a five-storey block of 23 luxury flats.

The company has already spent £1.6million on getting its plans through the initial planning process, and was granted permission in March.

A geotechnical survey has revealed a ‘sink circle’ beneath the site where a block of garages will sit.

If the hole collapses, 4,900 tonnes of earth would bear down on the building. Structural engineers have called for thicker walls to protect the new block- but have run into problems after trying to get permission to alter the plans.

Colin Felton, spokesman for the company, said: “We discovered a slip circle below the floor of the garage and sent the local authority a report saying there would 4,900 tonnes of cliff face bearing down on our building so we needed thicker walls.

“The council disagreed saying there was no problem with the cliff. Everyone is aware there is a problem except the council. It’s very disappointing.

“At the beginning Redap very much wanted to be part of the community but we were discouraged. It’s been one thing after another.

“It’s a long arduous process but we’re not giving up. We are still testing and may have a solution.

“We’re very committed but with obstacle after obstacle it seems hard for developers to do business there.”

The application was orignally refused by Southend Council last August, with the Swedish firm appealing.

In March, an almost identical plan was given the green light, while the appeal was still underway.

The development has no affordable housing, but the company offered £1.2million to shore up the cliffs behind the development.

It will also hand over £40,000 for public art and £14,000 to improve the road outside.

The development will have a restaurant on the ground floor and underground parking with 26 spaces.

The pub, which Redab is temporarily allowing to stay open, will be demolished in October.

A Southend Council spokesman said: “We understand that the applicant has been preparing detailed design drawings, which should take into account any structural issues associated with the building’s location. We will review further details on receipt.”