A person can only be detained and held by the police for up to 24 hours without being charged with anything.
The police must charge you with something if they plan to hold and detain you longer than 24 hours.
Although if you're suspected of committing a serious crime such as murder they can apply to hold you for up to 96 hours without being charged.
And if your crime falls under a Terrorism act then the police can detain and hold you for up to 14 days before they charge you with the crime.