detention WAS permitted under the British law BUT that bit of the law is in breach of ECHR
Essentially, yes. This is the closest a UK Court can get to striking down a law. Given the principle of Parliamentary Supremacy no law can be "illegal" or "unconstitutional". Law is defined as whatever Parliament enacts and the Crown assents to (Liz 2 signs it).
All a Court can do is rule that Parliament has enacted two incompatible things: in this case the Human Rights Act and the cited Terrorism Act. An appeal to the ECHR won't change anything for the plaintiff because ECHR rulings can't change or override UK law either.
An incompatibility ruling notifies Parliament that it has two conflicting statutes on the books. It is up to Parliament to decide which one it wants to amend or repeal to fix that.
Biting the hand that feeds IT
