The Mayfair Hotel Megabuild

Although it looks like business as usual at Claridge's - one of London's most luxurious five-star hotels, set in the heart of Mayfair - beneath the surface of this iconic, elegant, exclusive hotel, filled with glamorous guests, who enjoy the finer things in life, is a busy building site. An extraordinary engineering project is underway, which seeks to add a five-story basement at the bottom and 72 new rooms and suites spread over three new floors at the top.

But the owners are insistent that the hotel must remain open throughout the build, with the guests oblivious to the noise surrounding them - leading the miners to tunnel by hand. Filmed over six years, this series follows the building team and the hotel staff as they try to complete the build with as little disruption as possible to the hotel's array of high-profile guests.

It's just over halfway through the seven-year renovation project, and the team have adopted unusual measures to make way for the next stage of the audacious build – a four-storey roof extension. Meanwhile, below ground, the basement reaches its fifth and deepest level after overcoming the challenges of groundwater and an underground river.

But then disaster strikes, as world events intervene. The Covid-19 pandemic forces the hotel to close for the first time in over a century, as well as derailing plans to complete the building work on time.

With the megabuild shell nearing completion, the hotel turns its attention to the interiors, employing some of the world's top designers and craftsmen to meet the expectations of their well-heeled guests. A highlight is the new penthouse. With a rumoured £100,000 per night price tag, it will span the entire rooftop of Claridge's and feature four bedrooms, a swimming pool and its own lake. Its look is the vision of renowned Parisian interior designer Rémi Tessier, who is determined to use only the rarest materials and has suppliers quaking under the pressure of his high demands.

Meanwhile, down in the basement, Claridge's first-ever spa is taking shape under the guidance of Inge Theron, who aims to combine imported scents from Kyoto in Japan with the latest skincare tech to provide an unrivalled experience. But she faces plenty of unexpected challenges. First there is the noise from tube lines that requires a rethink on the build and then, just weeks from opening, unprecedented levels of rainfall in central London cause the basement to flood and destroy much of what her team have been working towards.

If they can get the spa back on track, David Walliams is keen to take the inaugural dip in the hotel's first-ever pool, while on the roof, the last minute addition of a piano pavilion prompts a very special guest to do an exclusive, impromptu festive performance, just as the penthouse is ready to start welcoming its first overnight guests.