In a landmark court decision against Uber, the U.K. High Court has ruled that its business model is unlawful.

The decision — which reboots the application of London’s regulations around private hire vehicle contracts — has huge ramifications for how ride-hailing platforms like Uber can operate in the U.K. capital and how much U.K. tax they will pay.

The crux of the issue is the contract model Uber and many other ride-hailing platforms have been applying. (And, indeed, how London’s transport regulator, TfL, has been overseeing — or, well, failing to — their compliance with the law.)