The 55-year-old has been informed by Medway Council that approval is needed for the works that he carried out at his home in the grounds of the scheduled ancient monument of the ruins of Cooling Castle in Cooling, Rochester, Kent.
The application is a "retrospective application for extension to existing garden wall together with raised beds and parvis".
A heritage statement included in the application explains that while the castle ruin is a scheduled monument, the Manor House is not a listed building and dates back to the 18th century.
It states: "The wall and planters that have been built are directly to the north of the house in an area of garden adjoining the walled swimming pool courtyard where it has little impact on the setting of the scheduled ancient monument.
"Trial holes were dug that confirm that there is no significant archaeology below this garden area."
A design statement adds: "The new wall and planters create a cohesive and attractive garden area viewable from the main house and the adjacent swimming pool and annexe.
with the previous works on site.
"These new structures can only be seen from the curtilage of the dwelling itself and not from the wider landscape due to its existing mature foliage that surrounds the castle."
There have been no comments from members of the public about the application.
A Medway Council spokesman said: "The works that were carried out were undertaken by the owner
on the assumption that planning permission was not required. He was subsequently advised that this was not correct and submitted a planning application."
A decision should be made by the council by September 9.