A very, very, senior officer of the Metropolitan Police said to me in a nudge nudge, wink wink sort of a way: ‘It’s voluntary – until they say no!’

Now I suspect that, if asked, he would say he was joking – but I don’t think he was. I think that statement is a true reflection of the situation in an investigation taking place into a serial rapist in South London.

What this officer was referring to was the taking of DNA samples from members of the black community because a new type of DNA profiling has indicated the perpetrator is of mixed black origin. This is being done on a ‘voluntary’ basis from ‘persons of interest’. ‘Persons of interest’ are people who have a possible connection with the crime either through location, profession or some other connection which might indicate they could be a suspect.

This rapist has been committing the most horrific crimes against old women for twelve years now – and the police are absolutely and justifiably desperate to catch the perpetrator.

I have been pursuing, in my role as a member of the Metropolitan Police Authority, a number of legitimate concerns around the taking of these DNA samples and the testing of them. This is not just ordinary DNA testing (which simply answers the question – is this trace of DNA really from person A?).

This is DNA profiling and involves cutting-edge science to get someone’s genetic mix out of the DNA sample. The technique is in its early days, but already can identify the racial mix from four main racial groups.

There are around 900 ‘persons of interest’. One of the key issues for me has been that if the ‘person of interest’ declines to give a ‘voluntary’ sample, he has then received a letter from a senior detective saying ‘I am looking into the reasons for your refusal and will let you know of my decision’. That is a pretty intimidating statement in my view. It gets worse. Out of 125 initial refusals who got the letter – the police went on to arrest five men. Two of those changed their mind on the point of arrest and ‘volunteered’ their DNA. DNA was taken from those arrested.

It is so easy to say end justifies means. It is easy to see the argument that this crime is so horrific that it is right to take DNA voluntarily or otherwise. Don’t get me wrong. The police are doing a great job. But it is a complete misnomer to call this type of testing ‘voluntary’. It is clearly mandatory in practice.

Moreover, recent new legislation means that if you or I are arrested – we can be taken to a police station, our DNA taken from us and kept on record in perpetuity – even if we are not charged with any crime.

In practice, we are getting mandatory DNA testing and a national DNA database by the backdoor. Now, one objection to this is that such important decisions should be made up front and in a publicly accountable way. Balancing civil rights, personal freedoms and the fight against crime are tricky – which is all the more reasons why such decisions should not happen on the quiet and without proper public debate.

There is a risk of an over-reliance on technology. What happens if the police do succeed in testing all 900 persons of interest and the culprit is not amongst them. What is plan B?

Additionally, this cutting edge science appears to only be able to define a mix from black ethnic backgrounds at this point in time. Thus far the DNA test has not been able to distinguish within the White European race. Does this mean that this method of detection can only be used to catch black criminals? If it does – does that mean the police should stop using it as a detection tool as it discriminates against black criminals?

On top of all of this, there have been cases where DNA has not proved to be the infallible methodology we were all led to believe in and has been proven to have been corrupted within laboratories.

So – my view so far? We need a public debate on these issues. In particular, we need to look at what safeguards are needed to accompany this approach to crime-fighting – and whether they can be sufficient to overcome the risks which go with it.

Thin end and wedge are the words that spring to mind…