From the 1st Jan 2006 a police officer has the power to arrest anyone;
1.who is about to commit an offence
2.who is in the act of committing an offence
3.whom he has reasonable grounds for suspecting to be about to commit an offence
4.whom he has reasonable grounds for suspecting to be committing an offence
All offences are now arrestable. The triviality of the offence is inconsequential, and the final arbiter for the necessity of arrest is the arresting police officer.
Once arrested, not charged, you can be drug tested. This became law 1st Dec 2005.
Additionally the new powers introduce covert evidence gathering, including DNA, fingerprints, shoeprints and digital photographs.
A new stop and search power specifically for the under 18 year olds has been introduced, to search for fireworks.
Police may now apply for 'multi-premises' and 'all-premises' warrants which allows multiple access to premises owned or occupied by a suspect. These changes enable the police to apply for repeated entry warrants and extend the lifetime of warrants from 1 month to 3 months.
Police fishing expeditions anyone?