The basic limits are set out section 41 to 43 of PACE - Police and Criminal Evidence Act 1984 section 41, section 42, section 43. The maximum time is 96 hours and (usually) runs from the time of arrest.
When an individual is arrested under under terrorism legislation (e.g. Terrorism Act 2000 section 41) it becomes possible for detention to extend up to 14 days.
Ann Widdecombe:
On 9 July the former Member of Parliament






