A treasure chest of gold sovereigns is expected to make up to £100,000 when it goes under the hammer in Penzance tomorrow (Tuesday, August 5).

For sale at Hansons Cornwall, The haul includes rare, solid-gold proofs mostly from the reigns of Elizabeth II and Charles III. Amounting to some 300 coins, it was owned by the father of a Penzance property developer who hopes his dad’s canny collecting eye will cause plenty of interest among coin collectors.

The Royal Mint produced more than 100 unique proof coins during the reign of Elizabeth II, each commemorating different landmarks, such as her Diamond Jubilee or milestone birthdays.

But the top lot, expected to sell for £7,000 to £8,000, is a five-coin, limited-edition set of gold proofs, celebrating the 75th birthday of her son, Charles III.

The sought-after set is made up of a £5 gold proof of the new king; a gold £2 proof, celebrating the centenary of the Flying Scotsman; a similar denomination coin marking the life and work of JRR Tolkien; a gold proof 50p, honouring 75 years of the Windrush generation, and the same denomination coin marking 75 years of the NHS.

The vendor said: “They all belonged to my father who had been interested in coin collecting ever since he was a lad and went out looking for WWII shrapnel with a metal detector but came home with a pocketful of coins.”

But his interest in gold proofs only emerged during the last 10 years of his life, after the death of his wife.

The vendor, whose father died aged 88, continued: “Dad became a bit of a fixture at the Royal Mint where everyone knew him and even gave him personal tours. At one point they even let him strike a coin for my daughter. There are some real rarities in his collection and we hope they find a new home among true collectors.”

The sale, at Hansons Auctioneers’ saleroom on the Penzance harbour, also includes a set of 10 consecutive Queen Elizabeth II full-gold sovereigns which is expected to make £5,200-£5,500. A sovereign set, making the late monarch’s 95th birthday, is expected to sell for £1,000-£1,200.

The vendor, who asked not to be named, said: “Some of the sets are really rare – two being the only one of their type ever made. Others are from really limited editions of 25 or 99.”

Proof coins are the highest standard coin the Royal Mint produces and struck three times to produce a sharp, high-quality finish with a mirror-like background.

They are highly sought after by collectors for their collectable value as most are issued in limited quantities, as well as their precious metal content.

Better still if they come with the original certificate of authenticity, which verifies the coin’s legitimacy.

The vendor continued: “I have seven ring binders of certificates and invoices relating to the collection, so authenticity is no problem.”

Auctioneer Darren Ashley, from Hansons Auctioneers Cornwall, said: “This is a veritable treasure trove of a coin collection, and we are delighted to be able to offer it to serious coin collectors both locally and from around the world.”