St John's House: This is the proposed Gatsby-inspired mega mansion with 80 rooms that could become Britain's largest new home

It is currently just a plot of 60 acres of private parkland with a large stone barn on the edge of the village of Ramsden in Oxfordshire.

But the proposed estate is the result of nearly 25 years of planning applications and design work by the world-renowned architect Professor Robert Adam.

It will be the largest Palladian home built in the UK for more than 100 years.

And it is now on sale for £20m although the finished product is estimated to be worth more than five times that much.

Plans include an enormous master suite occupying the entire top floor, a grand ballroom and even an underground car museum to house 50 exotic motors.

The indoor sports complex will have a swimming pool, gym which overlooks the ballroom, leisure room, prep kitchen, bowling alley and a jacuzzi, sauna and steam room.

The lavish entertaining floor, known as a 'Piano Nobile', includes a formal dining room, music room, formal living room and games room which overlooks the orangery.

There will also be two gate houses, a self-contained guest gazebo, guest lodge and five bay garage.

Outside, the estate, which looks towards the Cotswolds, will have landscaped gardens, a tennis court and a second swimming pool.

The land and the property design which comes with it are being sold by Sotheby’s International Realty.

Managing director Guy Bradshaw said: "This sale provides the opportunity to create a significant and special home that once built, will be one of the UK’s most private and significant homes.

"It has taken over 20 years to secure comprehensive planning approval and we believe it will no longer be possible to build something of this stature in this location.

"If someone were to spend in the region of £50m on the build, they will have installed every conceivable security feature within the structure and the most spectacular interior finishes.

"This would make it not only the largest new home to be built in the UK for over a hundred years but also the only one built from the ground up.

"Designed by one of the most revered architects of our time, offering views that make you feel as though you are living within a Constable painting.

"Once complete, we expect the end value could be in excess of £100m”.

All principal rooms, terraces and gardens would offer ‘unrivalled views of the most spectacular uninterrupted landscape and sunset views across the Cotswolds.

The 'Piano Nobile' has been designed for entertaining with ‘exceptional ceiling heights’ and ‘enormous entertaining spaces’.

As well as this, the ballroom level - inspired by The Great Gatsby - provides a ‘grand’ reception room, bar, private cinema, as well as a professional 'event' kitchen.

If built to the approved plans, St John’s House could be likened to Updown Court, the 15-year-old mansion in Windlesham, Surrey, which is also set in 60 acres but is 25 per cent smaller than the proposed Oxfordshire pile.