> The UK claims sharing of things like Netflix passwords is illegal[0].
The newspaper article you linked to mentions the ICO talking about copyright law.
Personally I think it would be more of a clear-cut case under the UK Computer Misuse Act, "Unauthorised access to computer material":
A person is guilty of an offence if—
(a) he causes a computer to perform any function with intent to secure access to any program or data held in any computer or to enable any such access to be secured;
(b) the access he intends to secure, or to enable to be secured, is unauthorised; and
(c) he knows at the time when he causes the computer to perform the function that that is the case.
And in terms of somebody operating a password sharing website, "Making, supplying or obtaining articles for use in offence":
(1)A person is guilty of an offence if he makes, adapts, supplies or offers to supply any article intending it to be used to commit, or to assist in the commission of, an offence under section 1, 3 or 3ZA
(2)A person is guilty of an offence if he supplies or offers to supply any article believing that it is likely to be used to commit, or to assist in the commission of, an offence under section 1, 3 or 3ZA
(3)A person is guilty of an offence if he obtains any article—
(a)intending to use it to commit, or to assist in the commission of, an offence under section 1, 3 or 3ZA, or
(b)with a view to]its being supplied for use to commit, or to assist in the commission of, an offence under [F21section 1, 3 or 3ZA].
(4)In this section “ article ” includes any program or data held in electronic form.