With the new Serious Organised Crime and Police Act 2005 coming into force on January 1st 2006, there will be no such thing as arrestable offences.
All offences you will be able to arrest, but only the 'Indictable' ones will you be able to use sec 17 Pace to enter and arrest. (Indictable / either way offences).

No more sec 17 for TWOC, Assault police, disqual driving........ as these will revert back to the normal summary offences, as schedule 1 of Sec 24 arestable offences will be repealed.

Check it out. Sections 110-111.

http://www.opsi.gov.uk/acts/acts2005/20050015.htm

Yeah but how cool will it be to arrest someone for dropping litter or not wearing a seatbelt

Well it will certainly make a few more co-operative teenagers if they know they run the risk of potential arrest.

I'm aware of the concept of "arrestable offences" in English law but I would imagine it would be a major pain. In my jurisdiction the police can arrest for any offence but of course there are a range of General Orders from the Commissioner (which are just advisory but it's always a good idea to comply ) which "guide" members in the exercise of their very broad authority to arrest. Happily it works okay.