For my part, I literally left the UK in part because the industry there was so geared towards contract work or boutique contract houses as the only viable career path for senior developers. It’s just not for everyone. I like staying with a product team and building and owning stuff; I like companies that build their technology in-house rather than outsourcing; I like being able to shape what the technology team contributes to the business rather than respond to already-baked RFPs. I like stock-based comp.
The UK tech job market is very well suited to certain kinds of developers and certain kinds of relationships between businesses (and frequently government organizations) and their technology providers.
It’s not the only way though.