Ask Slashdot: Securing a Journalist's Laptop Against a Police Search?

Bruce66423 writes: In the light of the British police's seizure of a BBC laptop what is the right configuration and practices to ensure that such a seizure provides zero information to the cops? This post from Thursday might be a good place for some ideas, but that one's expressly about securing a Chromebook; what would you advise for securing a more conventional laptop? (Or desktop, for that matter.)