In some contexts verbal consent may be ethically preferable to written consent. Where possible this should include audio-recorded consent. In other circumstances, for example telephone interviews or some ethnographic fieldwork, this may not be possible.
There are also circumstances (such as research with users of illegal drugs or with political activists in some contexts) where written consent might also create unnecessary risks for research participants. Even in this last case a researcher should seek informed consent where possible to secure the trust and confidence of those involved, but care must be taken to ensure that consent processes (eg asking for written signatures) do not pose risks to participants. Where consent is not to be recorded or explicitly secured, a full statement justifying this approach should be submitted as part of the ethics review.