A retired decorator from Woking became a millionaire after his Pokémon cards fetched $2.1 million (£1.56 million) at Ewbank's in Send, Surrey, on 21 October, the auction house stated.

The seller, who wishes to remain anonymous, had stored the collection in his attic for 15 years after his son lost interest. One set bought for $400 (£300) sold for $100,500 (£75,000).

That was not the most expensive purchase of the day. The Legendary Collection Complete Master Set attracted a hammer price of $134,000 (£100,000), against an estimate of $20,100 (£15,000) to $26,800 (£20,000).

The lot contained all 110 cards, another 110 reverse holo 'Firework' cards and four box toppers. Its Charizard card was in near-mint condition.

Ewbank's head of trading cards, James Spooner, described the scale of the collection when the owner brought it forward for assessment.

'When we then discovered that he had 42 such sets, our jaws hit the floor. We got to sell 41 of them, and he kept one.'

The owner sought a valuation after reading in his local newspaper that a single Pokémon card had sold for more than $8,040 (£6,000). He had not realised the potential value of his own collection.

Pokémon is a Japanese franchise spanning trading cards, video games and animated television series. The seller's interest began when his young son collected cards and swapped them at school in the late 1990s. The father liked their appearance and considered whether they might also offer an investment.

He purchased cards through eBay from a seller in Malaysia who supplied complete sets. The seller subsequently offered him complete master sets, explaining that they had about two or three for each issue.

'I thought that it would be cheaper to buy the full set rather than keep buying sealed packs of random cards in hope that when you opened them you could complete a set.'

He identified his first purchase as the Sky Ridge Charizard set, costing around $400 (£300). His own collection was separate from the cards his son handled.

'He had his own cards, but he never got to touch these, I'm glad to say.'

The cards were carefully filed into bespoke Pokémon binders while still sealed.

The owner stated, 'I know people always talk about finding treasure in the attic, but in my case that is literally true. I had no idea what I had until the team at Ewbank's explained it to me.'

Ewbank's initially estimated that the collection could fetch up to $361,800 (£270,000). By the day before the auction, commission bids had reached $1.1 million (£825,000), Spooner stated.

YouTubers, collectors and investors competed for the cards. Andrew Ewbank conducted the sale himself, at the business established by his late father, Chris.

'The build-up to this sale has been phenomenal, and on the day it did not disappoint.'

He added, 'We had bidders from all over the world.'

Ewbank's described the auction as its most successful in more than 30 years in business. Saleroom attendance was higher than at any sale since before the COVID pandemic, Andrew Ewbank stated.