London is experiencing a mini-boom in gourmet burger places. While they may never proliferate like ordinary fast food restaurants, they’re starting to become a significant feature of London’s high streets and the go-to place for fast-casual dining.

Last week, Brits queued for more than a mile to get a taste of an In-And-Out burger. This week, BurgerFi, one of America’s fastest growing, all-natural "better burger" concepts, announced it will open its first London restaurant in Wembley Central Square, and in 2017 will open a restaurant in central London. Gourmet Burger Kitchen just opened its third West End store and shows no sign of slowing down.  here is all this demand coming from?

Research by Mintel confirmed that Brits are looking for a better burger, with 7% of Brits who’ve visited a fast food restaurant in the past three months saying they’ve switched to gourmet burger restaurants, and the number's even higher in the younger demographic: over one in 10 (12%) of users aged 16-34.

Mintel’s data indicates customers are looking to upscale their burger experience at fast food restaurants too, with 52% of UK consumers who’ve eaten or bought food from a fast food restaurant in the past three months saying they’d be interested in trying gourmet burgers from fast food chains.

McDonald’s is paying attention. Earlier this year, McDonald’s unveiled its “Signature Collection” of burgers in 400 UK markets. The burgers are thicker, made with better ingredients, freshly prepared when you order them and delivered to your table.

But even with these improvements, fast food is falling out of vogue as customers crave thicker burgers with fresh and exotic toppings.

Concerns about health inspire people to try better-for-you options.  A grass-fed tower burger may not have fewer calories than a Big Mac, but it is better quality meat, and the perception is that the toppings are fresher.

Customers are also turning away from fast food simply because they can afford better. Income growth encourages upscaling. And there are so many choices, like the Avocado Bun burger at Joe’s Southern Table and Bar near Covent Garden.

Gourmet Burger Kitchen distinguished itself by offering a full gluten-free menu, appealing to health-conscious customers. Earlier this month, even as it was opening new stores, GBK was snapped up by the owner of Wimpy, Famous Brands which, according to Sky News, viewed the purchase as an opportunity to go upmarket. GBK has grown to 75 restaurants since 2010.

American favorites are cropping up over London and beyond as well. Earlier this month L&G secured five new locations for American fave Five Guys, with still more locations planned.

Smashburger launched in the UK with 35 locations, and is still expanding as well.