Relaxed and relatively informal.
Panel members turned up in (dress) jeans and casual shirts. They were friendly and knowledgeable and seemed to be genuinely interested in their roles and the company.
There was an element of common sense in the interview as they said they could see what I had done by my CV rather than asking technical questions and were working on personality fit into the organisation. My opinion is that this needs to be measured with a few more technical questions as there are many people who pad their CV with work they haven't actually done.