Those calling for universal coverage forget the financial, practical and ethical problems of marching every small child and OAP down to the police station to be "swabbed". They forget security and accuracy risks that come from a gargantuan haystack in which to search for your needles. All it takes is a few mismatches or compromised samples and juries would become skeptical of the soundness of DNA.
It is extremely rare for a first time serious offender to be matched to a crime scene by an old sample alone. There is almost always enough suspicion coming from witnesses, victims, car licence plates etc. to justify arrest and DNA being taken. In some recent high profile cases the police ignored vital leads and simply failed to make arrests that would have stopped serial rapists in their tracks. Liberty once advised a woman who went through the ordeal of a post-rape examination only to learn that her medical evidence was destroyed so her attacker escaped prosecution. Police incompetence is an argument against a universal database, not for it.
The Human Rights Act protects our privacy but allows necessary, proportionate and lawful intrusion. So keep the samples of those under investigation and those convicted (even before DNA technology)of serious offences to which DNA is relevant. Obvious examples are sexual and violent crimes and burglary. That's far more practical than placing the entire population on a suspect database.