A millionaire property developer has admitted he should not have modernised the Grade II listed building behind the hymn All Things Bright and Beautiful.

Llanwenarth House was built in the late 16th century and was given its special status more than 60 years ago because of its national importance. The Georgian-style manor in the picturesque Usk Valley, south Wales, is where Irish composer Cecil Alexander is thought to have written the lyrics to the famous hymn.

Newport Crown Court heard that Kim Gregory Davies carried out dozens of unlawful alterations – including the installation of a “mosaic-clad jacuzzi”, replacing timber windows with “modern” ones and removing staircases.

The 60-year-old, of Govillon, Monmouthshire, had previously denied any wrongdoing and insisted the changes he made were within the rules.

However, he has now has pleaded guilty to five charges under the Planning (Listed Buildings and Conservation Areas) Act 1990.

His legal team asked Judge Daniel Williams to defer sentencing so Davies could “put things right”.

Defence counsel George Carter-Stephenson QC said: “My client accepts that he has got himself into a very difficult position by fighting this case.

“He now has accepted legal advice and has pleaded guilty to these offences and needs to do something positive to restore the house to the way it should be.

“He wants to put right what he has wrongly done to the house.”

Davies bought Llanwenarth House for £675,000 – but was asking £2.25 million for it when putting it on the market four years later after spending a seven-figure sum on its restoration.

However, the court heard the renovations – which took place between June 2006 and August 2012 – had been “deliberate breaches” of planning law and the strict rules designed to protect listed buildings.

Other alterations to Llanwenarth House included replacing old doors with modern “Tudor-esque” ones, installing ceiling spotlights and turning a bedroom into a bathroom.

Davies also admitted offences relating to the property’s Coach House and its courtyard – such as tearing up old cobblestones and putting down new flagstone paving.

Having examined the sentencing guidelines, Judge Williams decided against deferring his judgment on the case.

Penalties for changing a Grade II Listed Building without permission include a maximum 12-month prison sentence or an unlimited fine.

Prosecutor Nicholas Haggan QC said that costs in the case were also likely to be “significant”.

Davies was released on bail ahead of sentencing on May 15.