For 20 years the website BrickLink has been the best kept secret in Legoland, used by superfans to track down those elusive missing pieces and trade coveted minifigures for big profits.

Nicknamed CrackLink, it is the world’s largest online community of adult brick fans – called AFOLs [adult fan of Lego] in Legospeak – who, with more than a week’s pocket money to burn, are important customers for the world’s biggest toy company.

But last month online brickhead forums and blogs lit up after it was announced that the Danish toymaker had taken over the site, giving it a foothold in this lucrative secondhand market and a chance to see inside the heads of a passionate fanbase.

The fallout from the deal, for an undisclosed sum, has seen Lego accused of “muscling in” on fan culture and concerns voiced that the ownership change will result in higher brick prices. With 600m listings, elements tend to be 10-20p cheaper on BrickLink than Lego’s own spares service.

Adam White, editor of the Bricksfanz site, said fans’ reaction had been mostly negative. “It’s because BrickLink was an independent platform,” he explained. “Lego has its own part ordering service, but it sets the prices and the range is not as big. People are asking: are prices going to go up? I don’t think Lego is a big bad corporate but everyone thinks this is about cleaning up in the secondhand market.”

Today Lego is as likely to be on an adult’s Christmas list as a child’s. The brand has enjoyed big hits this year with models inspired by TV shows such as Friends – the Central Perk cafe, which comes with a 4cm high plastic Ross and Rachel, has been a blockbuster success – and Stranger Things. The toymaker has also released a mindfulness book called Build Yourself Happy: The Joy of Lego Play, with John Lewis reporting sales of premium sets – such as the 6,000-piece Taj Mahal – up 25% in 2019 as more Britons discover or rediscover bricks.

But many adult Lego fans prefer free play, creating elaborate models (my own creation or MOC in Lego parlance] that belong on an episode of Lego Masters. They sell instructions for these unofficial sets, which range from an epic “Hogwarts diorama” to souped up Batmobiles. There are close to 20,000 MOC designs listed on BrickLink and fans fear this unauthorised creativity is vulnerable with “Big Brother” watching.

But Lego, which sells £4bn worth of plastic bricks a year, has batted away such concerns. Owning BrickLink is about “strengthening” ties with its 1.1 million members not destroying them – not least given the company’s overarching goal of fostering creativity.

Lego’s chief marketing officer, Julia Goldin, says the site will continue to run independently from its US base. “It has been a very effective marketplace, so you don’t want to interfere with that,” she explained. “We will always listen to fans. This is about getting much closer and understanding what the community needs in order to continue expanding and thriving.”

Lego, which is controlled by the billionaire Kristiansen family, was forced into a major rethink in 2017 after suffering a rare slump in sales and profits. The Billund-based company confessed it had become too bureaucratic and its product development poor at a time when the toy industry is battling the internet for kids’ attention.

The toymaker has been investing in “digital play experiences”, such as the Hidden Side series which combines its plastic bricks with an augmented reality app – effectively enabling children to bring their models to life. Recent toy sales suggest Lego is back on song, with Harry Potter-themed sets and a £160 Land Rover Defender kit among the most sought after toys this Christmas.

Lego’s 2017 wake-up call may explain the company’s interest in a niche site like BrickLink which was started in 2000 by Dan Jezek (an AFOL who wanted to find others). In 2013 the site was sold to NXMH, a business owned by the Korean entrepreneur Jung-Ju ‘Jay’ Kim. The scale of transactions on the site is not known but over the years it has grown in stature, building a network of 10,000 sellers in 70 countries.

The jury is still remains out though. “This is terrible news,” writes Peppermint_M, in a thread on the Eurobricks forum. “Nothing good can come of a monopoly on brick sources.” Another suggests it could spell restrictions for sellers and “might make many of them close their shops”.

But Minifigforlife owner Andrew Watts, who has been selling on BrickLink for nearly 17 years, is sanguine about the deal. Yes it gives Lego a stake in the secondhand market, he says, but eBay and Facebook are far bigger markets for used bricks. He suggests the biggest prize is the treasure trove of data provided by the site’s passionate users – and also sees room for improvement because the site is hard for the uninitiated to use.

“Secondhand sales to AFOLs will give Lego quality data about what sells and how often,” says Watts. “This information can improve its knowledge of what is popular and to perhaps bring back parts and themes that they had written off.”

There have been skirmishes between Lego and the strident AFOL community before, Watts adds. In 2004 Lego tweaked the colour of grey and brown bricks to make them more appealing to the children: “To this date this has been the change that infuriated the community the most.”