Planning permission has been granted to build Britain’s largest new home in the countryside.

A plot of land, with plans to build an extravagant 68,000 foot mega mansion, has gone on the market for £20 million.

The enormous home will boast more than 80 rooms with two pools, a bowling alley and a car museum – and is set to be worth more than £100 million once built.

St John’s House will be set on the edge of the village of Ramsden in Oxfordshire and cover the equivalent floor space of more than 60 average-sized family homes.

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The plot of land, which is currently made up of 60 acres of private parkland with a large stone barn, is on sale for £20 million – but the the finished product is estimated to be worth more than five times that amount.

The proposed estate has come as a result of nearly 25 years of planning applications, with design work done by world-renowned architect Professor Robert Adam.

Once constructed it will be the largest Palladian home built in the UK for more than 100 years.

Plans for the incredible home include an enormous master suite that will span the entire top floor, a grand The Great Gatsby-inspired ballroom and even an underground car museum with space for 50 vehicles.

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

The lavish entertaining floor, known as a ‘Piano Nobile’ will feature a formal dining room, music room, formal living room and games room which overlooks the orangery.

Its ballroom level – inspired by The Great Gatsby – will provide a ‘grand’ reception room, bar, private cinema, as well as a professional ‘event’ kitchen.

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 ‘unrivaled 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’.

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.