A Police Officer may without warrant enter any premises where he has reasonable cause to suspect that a person is within/upon those premises that is wanted for an 'Arrestable Offence' or Wanted on Warrant for an Arrestable Offence. Warrants come in many different ways also. Some carry powers of arrest and some dont. Some of those that do carry a power of arrest may only have a limited power of arrest and the person must be released almost immediately after arrest and their address confirmed (Bail Warrant). Other warrants allow a person to be arrested and held to be put before the next availbale court. This ns know as a 'No-Bail Warrant'. No entry can be gained for summary offences like 'Driving without a Licence' for example.
Interesting piece but this passage is wrong, police do not have the right to enter property for those 'wanted for an arrestable offence'. The wording should be that they have a power of entry for those suspected of an indictable offence. Therefore quite rightly, they DO NOT have a power of entry for summary offences i.e matters which can only be heard in a magistrates.
Please see the videos below for the case in point; unlawful police entry
http://www.youtube.com/watch?v=Lx0rFqidrAI [part 1]
http://www.youtube.com/watch?v=m2CTDsnH2R4 [part 2]