CNN  — 

A collection of rare Rolls-Royces, including vehicles used by Queen Elizabeth II and Princess Diana, is to be auctioned off in the UK.

The eight cars are expected to attract combined bids of up to $6.4 million (£4.9 million) when they go under the hammer next month, according to estimates from Bonhams auction house.

Among the most anticipated lots is a 1953 Rolls-Royce Phantom IV State Landaulette, used by the Queen on state occasions and kept by the British royal family for more than 40 years. The vehicle, which has a top estimate of $2.6 million (£2 million), is the same model as the one used by Meghan, Duchess of Sussex, on her wedding day in May.

“There were only 18 of the Phantom IVs built, and they were bought by heads of state or dignitaries,” said Bonhams’ co-chairman, Malcolm Barber, in a phone interview. “None are exactly the same, and they’re all built to special order. Even if you are a Rolls-Royce collector, you wouldn’t have anything similar, because each has its own identity.”

US actress Meghan Markle (C) walks down the aisle in St George's Chapel, Windsor Castle, in Windsor, on May 19, 2018 during her wedding to Britain's Prince Harry, Duke of Sussex. (Photo by Danny Lawson / POOL / AFP)        (Photo credit should read DANNY LAWSON/AFP/Getty Images)
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Rolls-Royce has been a carmaker of choice for British royalty since the 1950s. Another three of the eight vehicles on auction were either owned or used by members of the Windsor household, according to Bonhams.

Among them is a rare 1960 Phantom V State Limousine, which has attracted an estimate of $1.3 million to $2 million (£1 million to £1.5 million). A 1985 “Centenary” Silver Spur Saloon used by Princess Diana is expected to sell for $197,000 (£150,000) or less.

Billed as a “Heritage Fleet” by Bonhams, the cars are being made available by Bentley, the luxury British manufacturer that split from Rolls-Royce in 1998.

Barber claimed that it is “very rare to see royal household cars come on the market.” But other notable Rolls-Royces will also be available in September’s auction, including a vehicle with the custom license plate “RR1” and a number of cars that were the last of their type to be built at Rolls-Royce’s historic factory in Crewe, Cheshire.

“As we’ve seen over the years, when cars have celebrity or important provenance, then – compared to others similar – there is a premium to pay,” Barber said. “(But) they are bespoke, coachbuilt cars that are important in their own right.

Interior of the 1950 Rolls-Royce Phantom IV State Landaulette.

“And if you are a Rolls-Royce collector, then the ‘last-of-the-line’ models may fill in the missing piece of the jigsaw.”

The vehicles are among more than 50 being auctioned off by Bonhams at the Goodwood Revival motoring festival near Chichester in West Sussex. Other lots include a 1964 Ferrari 250 GT Lusso, which is estimated to attract bids of up $2 million (£1.5 million), and a Bugatti Type 30 dating back to 1922.