Inside one of London's most expensive homes – including a $1.2 million staircase

Renovations are often a lengthy, costly affair – but not as much as this one.

In Central London sits Amberwood House, a six-storey, 15,300 square foot mega mansion originally built in 1928.

As the former Panamanian Embassy and home of ballerina Margot Fonteyn, parties at the property hosted a slew of renowned figures including Princess Margaret and John F Kennedy.

Stream episodes of Britain's Most Expensive Houses for free on 9Now.

In an episode of Britain's Most Expensive Houses – which you can stream for free on 9Now – cameras go inside the massive property just before completion of a four-year-long renovation, offering a glimpse at what will become one of London's most pricey real estate listings.

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In a mansion of seven bedrooms and bathrooms, it may be surprising to learn that the central feature is in fact a staircase.

Inspired by the former ballerina owner dancing on the stairs, property developer Kam said he was determined to make the staircase a feature across all six floors.

But that came at a cost – $1.2 million, in fact.

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To restore the house to its former luxe appeal, it also featured $10,000 bespoke taps and a basement spa with gym, sauna and 12-metre swimming pool.

The full renovation was budgeted at an eye-watering 58m.

"There's no doubt about it that he's spent a lot of money. Everything has simply been carefully handpicked," reacted potential realtor Diana reacted.

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Developer Kam said the "very special home" would be listed with, unsurprisingly, a very special price tag as well.

"We've discussed the guide to be circa £75 million (AU$155 million)," he said.

The home also featured a private outdoor entertainment area in the heart of London.

See more of the costly property in Britain's Most Expensive Houses Season 1 Episode 5 on 9Now.

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Stream episodes of Britain's Most Expensive Houses for free on 9Now.