In the first place, they had no right to detain the personal property. I wish the officers joy in explaining why he thought these items were "evidence in criminal proceedings" or were relevant to a "deportation order".
You misread it. It takes practice to read legal documents and you made a common error. You missed the 'or'. Case (a) is in use right now, but it has a 7-day clock. Case (b) or (c) would be used if they want to hold something indefinitely.
My suggestion for reading legal documents would be to be very, very careful about punctuation and ands/ors. Highlight or underline them if you need to.
In the second place, nothing I can see therein allows them to destroy detained property, which is a very extreme response under any cricumstances. It also contradicts the intent of the section, which was to allow collection of property to be used as evidence.
This is a different case. The destruction of hard drives was done by GCHQ at the Guardian UK offices well before David Miranda was detained by the police. There is no evidence that any possession of Mr. Miranda has been destroyed. But when he gets them back, I'd assume that they were loaded with spyware.
Pretty ironic since the preamble states that the Act was "An Act to make provision about terrorism; and to make temporary provision for Northern Ireland about the prosecution and punishment of certain offences, the preservation of peace and the maintenance of order.". The only terrorism here I see is committed by the government.
This is an insanely broad law. Look at Section 2:
Power to stop, question and detain
2 (1) An examining officer may question a person to whom this paragraph applies for the purpose of determining whether he appears to be a person falling within section 40(1)(b). (i.e. a terrorist)
(2) This paragraph applies to a person if--(a) he is at a port or in the border area, and (b) the examining officer believes that the person's presence at the port or in the area is connected with his entering or leaving Great Britain or Northern Ireland [or his travelling by air within Great Britain or within Northern Ireland].
(3) This paragraph also applies to a person on a ship or aircraft which has arrived [at any place in Great Britain or Northern Ireland (whether from within or outside Great Britain or Northern Ireland).]
(4) An examining officer may exercise his powers under this paragraph whether or not he has grounds for suspecting that a person falls within section 40(1)(b).
What does this mean? At a port of entry the cops can detain you without suspicion to determine if you might possibly be a terrorist. Basically, they can detain you for any reason whatsoever.