If Sydneysiders thought property prices had hit peak ridiculous, licence numberplate collectors have gone one better with the original NSW No.4 plate up for sale for between $1.2 million and $1.4 million.

The asking price tops the $1.18 million median house price in Sydney, and doesn’t even include the Rolls-Royce that it was attached to until early last year when it was owned by Aussie John Symond.

The founder and executive chairman of Aussie Home Loans bought it in 2010 from property developer, Ivan Holland, who had secured it in an art swap from businessman and art collector John Schaeffer.

Aussie John was approached to sell the 1910-registered plate early last year, but with a $1.2 million price tag the buyer from Asia declined.

Mr Symond has confirmed he sold the plates some 18 months ago. were bought by a mystery buyer in South Sydney.

Numberplate aficionado Shane Moore said the plate is widely rumoured to have been sold by Mr Symond for about $1 million.

“Single-digit plates rarely trade so quickly. They are usually held within the one family for decades,” said Mr Moore, who runs the numberplates.com.au website.

“As an asset class they’ve appreciated in value in recent years, but they’re also a volatile asset. If things go badly, investors will sell off the plates,” Mr Moore said.

Registered in 1910, the No.4 licence plate is the most expensive item set to go under the hammer on August 28 at the 2017 Shannons Sydney Winter Classic Auction.

It tops the asking prices for 26 cars on offer, including a 1924 Rolls-Royce for $120,000, a 1964 Porsche for $125,000 and a Mustang Fastback for $120,000.

Single-digit, heritage licence plates have long been a highly prized collectible among the ultra-wealthy. In 2008, the No.6 NSW number plate sold for $800,000. It topped the previous high of $683,000 paid in 2003 by an Asian businessman for No.2.

The No.1 plate is owned by the family of the late founding chairman of Australian National Airways, Sir Frederick Stewart, who had owned it since the 1930s.

The No.8 plate was regarded as the most valuable because it is regarded as auspicious in traditional Chinese culture. It last traded in 2010 for $500,000.

In Victoria, single-digit number plates are also investment-grade assets. The number 1 VIC plate is owned by former Foster’s Group chief Peter Bartels.

In 2013 British businessman Afzal Kahn knocked back £8.5 million for his “F1” numberplate, having bought it for a record £440,000 in 2008, according to The Telegraph in London.