GOV.UK Frontend is already fully open source [0] with comprehensive documentation [1] and GDS encourage community contributions, libraries and resources [2]. If there was any worry about phishing that would be a question for GDS
This is impressive Matt, and I love the design system GDS has developed, but I'm not sure they want non-government services to use the system. From the second link you posted:
> Use this design system to make *government* services consistent with GOV.UK
Emphasis mine. Are GDS aware of this work? I am in no way affiliated with GDS by the way.
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I'm always wary of this kind of thing not being on a gov.uk domain, which in this case is entirely appropriate because it's not in anyway official or endorsed by GDS. Not for any direct phishing/crooks concerns as raised above, but because it waters down the impact of this kind of thing always being on gov.uk domains.
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Edit: I'd be _very_ surprised if GDS don't take issue with you having "GOV.UK" in the name given that it is no way associated with gov.uk
Phishers probably wouldn't even bother using a vue component - it's easier to copy the whole page from dev tools body.innerHTMl