Although the legal requirements aren't specific, my concern would be that the Examiner, in reading the consultation summary, may want to know who responded and who the comments on the main issues were attributed to, so that there was a clear audit trail if the consultation process was queried through the post-submission consultation run by the LPA. It is also helpful if the comments made by organisations (especially the statutory consultees) can be clearly identified.
In my experience the main reason for local people wanting confidentiality in consultations is because they are concerned that people won't otherwise respond because they are objecting to issues that are supported by the people that they live / work / socialise with. Our advice (in local plan consultations) to those people is that they can always approach their local councillor and ask them to submit a comment picking up on their issues on behalf of their constituents.
However the neighbourhood planning process is slightlly different, and if the group had decided to run a drop-in event during their pre-submission consultation with (for example) comments captured on post-it notes - I would think this clearly should count as part of the consultation and should be recorded as such (making clear which comments were received this way). This could be a way to get around the confidentiality issue for some.
At the end of the day it is about having a suitably clear audit trail to explain the actions taken, responses received and how these were considered, clearly, in the consultation summary.
