D.B. linked to the Wikipedia page for the UK DNA Database,
which ties in nicely with the research I've been doing, as it links to the case of S and Marper v. United Kingdom.
In this case, the European Court of Human Rights held that holding DNA samples of individuals arrested but who are later acquitted or have the charges against them dropped is a violation of the right to privacy under the European Convention on Human Rights. It is interesting to note that in the judgement,
the court commented in paragraph 119 that:
In this respect, the Court is struck by the blanket and indiscriminate nature of the power of retention in England and Wales. The material may be retained irrespective of the nature or gravity of the offence with which the individual was originally suspected or of the age of the suspected offender; fingerprints and samples may be taken – and retained – from a person of any age, arrested in connection with a recordable offence, which includes minor or non-imprisonable offences. The retention is not time-limited; the material is retained indefinitely whatever the nature or seriousness of the offence of which the person was suspected. Moreover, there exist only limited possibilities for an acquitted individual to have the data removed from the nationwide database or the materials destroyed (see paragraph 35 above); in particular, there is no provision for independent review of the justification for the retention according to defined criteria, including such factors as the seriousness of the offence, previous arrests, the strength of the suspicion against the person and any other special circumstances.
It also uses paragraph 125 to state:
In conclusion, the Court finds that the blanket and indiscriminate nature of the powers of retention of the fingerprints, cellular samples and DNA profiles of persons suspected but not convicted of offences, as applied in the case of the present applicants, fails to strike a fair balance between the competing public and private interests and that the respondent State has overstepped any acceptable margin of appreciation in this regard. Accordingly, the retention at issue constitutes a disproportionate interference with the applicants' right to respect for private life and cannot be regarded as necessary in a democratic society. This conclusion obviates the need for the Court to consider the applicants' criticism regarding the adequacy of certain particular safeguards, such as too broad an access to the personal data concerned and insufficient protection against the misuse or abuse of such data.
In the following paragraph, they conclude that there has been a violation of Article 8 of the European Convention on Human Rights.
As Article 8 is based on privacy, and given the finding that the database "fails to strike a fair balance between the competing public and private interests", plus the repeated stressing of the blanket and indiscrimate nature of the database, this strongly suggests that a mandatory DNA database of all citizens would also be in violation of Article 8.
I've also found a follow-up judgement from the UK Supreme Court, in the case of R (on the application of GC) (FC) (Appellant) v The Commissioner of Police of the Metropolis.
Unless you're really interested, it's not worth plowing through the whole thing, as confirms the result of S and Marper v The United Kingdom (2008), finding that the police policy of retaining DNA breached the Article 8 right to privacy. What is
interesting is very near the start, on page 3, paragraph 1:
There can be no doubt that a national database containing the data of the entire population would lead to the conviction of persons who would otherwise escape justice. But such a database would be controversial. It is not permitted by our law.
So, a mandatory DNA database is not allowed under UK law, and any attempt to introduce one would breach Article 8 of the European Convention on Human Rights.
I also attempted to find some information comparing the proportion of a country's population on a DNA database with the proportion of crimes solved in that country, but failed to come up with anything. I did find this
article from the Times (a respectable broadsheet newspaper), which states that:
More than one million new DNA profiles taken from individuals or the scene of crimes have been added to the database over the last two years bringing the total to more than 5.6 million.
Over the same period of time the number of crimes solved where a genetic match was available fell by 16,000, according to the 2009 report of the operation of the database.
While this isn't the hardest of evidence, it does suggest that adding more people to a DNA database does not necessarily lead to more crimes being solved.