A retired Surrey decorator is set for a £250,000 payday after a Pokémon card collection kept in his loft for 15 years turned out to be hugely valuable.

The collector, who does not want to be identified, had no idea what he was sitting on until he spotted a newspaper article about a single Pokémon card selling for more than £6,000.

He realised he owned several cards of the same type and took a sample of his collection to Ewbank’s Auctioneers, based in Send, to have them assessed.

“When we saw what he had, all in mint condition, we couldn’t believe it, or the fact that he had no idea what they were worth,” said James Spooner, head of trading cards at Ewbank’s.

“When we then discovered that he had 42 such sets, our jaws hit the floor.”

The collection is now expected to fetch up to £250,000 when it goes under the hammer next month, although Mr Spooner believes the final total could be even higher.

“Even with that, this is easily the most valuable collection we have handled so far, and it could go as high as around £270,000 hammer,” he said.

The remarkable collection began because of the decorator’s son, who became caught up in the Pokémon craze sweeping playgrounds in the late 1990s.

“When my son was young, in the late 1990s, he started getting cards and swapping them at school. I thought they looked nice and wondered whether they might be a good investment,” said the decorator, who lives in Woking.

“I was lucky enough to find someone in Malaysia who sold complete sets, and I bought a couple of things from them on eBay. They then asked me if I would be interested in buying a complete master set of Pokémon cards as they had about two or three master sets 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.

“The first set I bought cost me around £300. It’s the Sky Ridge Charizard set and Ewbank’s have estimated it for the sale at £20,000-40,000.”

The cards were carefully placed in bespoke Pokémon binders while still sealed and in mint condition.

When his son eventually lost interest in Pokémon, the collection was put away in the attic, where it remained for around 15 years.

Crucially, his son had his own collection to play with while the potentially valuable cards remained untouched.

“He had his own cards, but he never got to touch these, I’m glad to say,” said the collector.

“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 has been staging dedicated trading-card auctions for five years, with sales totalling more than £1.1 million, but says the Woking man's collection is the most valuable it has handled.

It is also the second valuable Pokémon collection to emerge from a Surrey attic and reach the auction house this year.

Teacher Andrew Braund approached Ewbank’s in April with a 20-year-old collection of Pokémon cards he had stored in his parents’ attic.

Three of his rarest cards sold for a combined £32,800 on April 16, with Mr Braund using the proceeds towards his August wedding to Rachel Moseley.

Auctioneer Andrew Ewbank said: “From vinyl records and vintage posters to retro video games, action comics and trading cards, we have focused on developing Popular Culture sales over the past decade and now lead the way in the UK outside London.

“This has enabled us to attract a global following for our auctions, especially as you can bid live online from anywhere in the world, and this is now paying off with exceptional prices.”

The Woking collector's 42 sets will form a single-owner auction titled Pokémon: A Decade of Masters (1999-2009) on October 21.

Live bidding will be available through Ewbank’s website at www.ewbankauctions.co.uk