I’ve tried to find some advice on the great Google, but I just find it vauge and contradictory at best.
That’s not the advice at fault. It’s the implementation which is absolutely “vague and contradictory at best”.
The rules are pretty simple, duty at whatever the appropriate % is (6% on 87149990, but it’ll depend on what it’s declared as by the shipper), VAT at 20% on the full value inc duty and shipping.
Under £135 this should be paid by the dispatcher, over that it’s down to you. It’ll be taken care of by the shipping company on your behalf, and they’ll charge you for that.
In practice you may pay nothing, some or all of that. The goods might be misdeclared and you might end up paying 1% or 101% duty etc, which is why the advice, broadly nothing more than anecdote, is vague and contradictory.
It will eventually settle down but for now its a lottery.