In the Vale of Glamorgan, agents Sorcha Rodbard-Hedderwick and Jemma Friday are marketing £2.2 million Llwynhelig House - a Grade II-listed manor featuring a log cabin and shepherd's hut. Broker Margaret Thompson is in Jersey to showcase £17 million Sunningdale Manor, which has undergone a multimillion-pound renovation. In London, agent Constance Cunningham presents three high-end apartments to Argentinian lawyer Ramiro, and in Cornwall, Ian Lillicrap returns to the charming village of Flushing, where he's been called to value a 16th-century house that he's sold twice before.

Broker Constance Cunningham has the chance to sell the state-of-the-art £60 million London property the Penthouse at Park Modern, while Emma Brooks takes on Shellingford House, a £3.75 million Cotswolds manor house with a secret garden. Adrian Dunford calls on his team to help sell a £14.95 million property in Sandbanks in Poole, the UK's most expensive costal area, and in Oxfordshire, independent agent Tim Phillips searches for a quintessentially British family home for an Anglo-American family.

Fine & Country agent Margaret Towey is selling £10 million Hertfordshire property Orchard View - a hi-tech home that might be perfect for retired model Jilly Johnson, who wants to downsize. However, it has also attracted filming locations manager Lexi, who is scouting it for a potential movie. French Alps-based real estate agent David Lucas is in London trying to sell two luxury chalets in Val d'Isère, while Fine & Country agent Greg Perrins is hoping to sell The Common, a 10,000-square-foot property listed at £3 million.

Raj Gill, managing director of Knightsbridge Prime Properties, is under pressure to sell a recently renovated £18 million townhouse near Harrods while managing its lucrative rental income of £27,000 per week. In Buckinghamshire, Fine & Country agent Haydn offers an indecisive client the choice of a wing of a listed mansion, a converted farmhouse and a seven-bedroom rectory. In Stratford-upon-Avon, agent Jonathan Handsford prepares to list Birgan Lodge, a new three-storey home with a private jetty onto the Avon river.

Broker Mark Coulter hopes a glowing review will sell £3.5 million Ormiston Castle close to Edinburgh, and Ian Lillicrap lists a five-bedroom Cornish cottage with 11 acres and stunning coastal views. Fine & Country's managing director Nicky Stevenson visits Jersey's most exclusive properties with broker Margaret Thompson, of Real Housewives of Jersey fame. Their aim is to find a buyer for £21 million Cardington House, a mega mansion with direct beach access.

Britain's Most Expensive Houses is back with a new series, as we take an exclusive peak into the country's most extraordinary properties with eye-watering price tags. From London's most coveted postcodes to grand country estates and coastal retreats, we delve into the pockets of the uber-wealthy and follow brokers as they manage multi-million-pound deals. In this first episode, top broker Josh Marks has secured the most expensive property on the open market in Britain: an £80 million penthouse in Knightsbridge. But with only six months exclusivity and a tiny pool of potential buyers, he needs to dig deep into his elite network to close a deal. In Cornwall, Ian Lillicrap is showcasing two prime properties: a £4 million coastal home with stunning views over St Ives Bay and a £1.85 million Californian-inspired retreat. Can he impress buying agent Clary Coode and achieve a double deal? And agent Tim Phillips is bringing Lynford Hall, a 20-acre country estate built in 1856 in Norfolk, to market. It's being positioned as a commercial or residential opportunity, but can Tim find someone with deep enough pockets to take on this unique estate?