I used to be a senior Civil Servant….

[CurlewKate]

….and what I want to know is how the hell are they going to implement the tariffs so insanely quickly? Particularly considering the cuts the Trump administration has implemented.

It's pretty simple, you just apply the tariff as part of the import fees based on the source location (or port of loading) of the container. If the paperwork is incorrect you don't unload it or impound it until said fees are paid.

The real issue is sorting out the stuff in transit to the US as that won't have the correct paperwork but after 6 weeks or so that will be resolved.

In practice it won't be "pretty simple". Look at what happened with Brexit and the ports here.