Now an application for retrospective permission for the cavern has been made by the resident in Sefton, who is creating the garden structure complete with an access staircase and a water feature.

According to documents submitted as part of the planning application, work began on the unusual development in 2018. The cavern sits to the rear of the house on Pershaw Grove in Ainsdale.

Photographs show a garden pond complete with a model bird leading to an ornate stone-built wall, described in the documents as a “ruin” with no roof. Behind the “ruin” sits a patio area with a statue of a man appearing deep in thought. Next to the pond is a small bridge which appears to run across towards the stone-built wall. Two waterfalls are also included in the design.

Another photograph shows work in progress on the design with a large open hole sitting to the left of the bridge. Another walkway across the hole in the ground is depicted with construction materials piled up on the patio area beyond.

A third photograph depicts a stone archway under construction to the left of the underground cavern which appears to lead towards a garden outbuilding.

A drawing submitted as part of the application shows close to the archway a series of steps leading down to a passageway that in turn leads into the underground cavern, which sits just beyond the pond.

According to an application form submitted as part of the permission request, work was completed on the structure in June.

Pre-application advice was sought from Sefton Council, with the applicant stating they were advised: “The proposal is generally acceptable in terms of design and it is unlikely to have a detrimental impact on the living conditions of neighbouring residents.”

The application is currently open for comments, with a decision expected on whether the owners are allowed to keep their unusual garden design by October.