Reasonable suspicion?
Under Code A of PACE, this must be based on fact, intelligence, information, or behaviour. Sufficient grounds include - matching a description of a suspect; intelligence linking suspect to an offence; suspicious behaviour. Searches cannot be based on race, religion, physical appearance or previous convictions. These are not sufficient grounds. Reasonable suspicion must be judged objectively - not purely on what the individual officer believes - there must be something that objectively justifies the search (Castorina (1988)).
If these requirements are not complied with, the search is unlawful as seen in - Osman v DPP (1999) - Osmans search was unlawful because the police officers who searched him did not give their names and station, contrary to the requirements under PACE 1984.