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I support Ron Iphofen's call for a common ethical practice code in the social sciences ("Do the right thing - unite", 14 January), but I found the objections raised in the letter the following week from Ken Smith, a senior lecturer in criminology, very odd. He does not seem to know that most ethical codes already dispense with the need for fully informed consent when it is likely to prejudice the validity of the research.

In such circumstances, it is widely accepted by all ethical codes that covert surveillance may sometimes be essential if the truth is to be revealed. This is because the most important ethical principle of all is that research must be valid and reliable. When it is not, all participants and the public recipients of such research are abused. Indeed, this is endorsed by the ethical code published by the British Society of Criminology.

Paul Kiff, Graduate School, University of East London.