From my experience the 'interviewers' are juvenile females that are in 'senior management ' positions. They cannot spell and have very poor standards of literacy. Their 'management style' is one of play on the computer or mobile, hide in the office, ignore staff (apart from favourites) and generally treat their team like dirt.
Challenging but not frustrating.
It's held by 3 interviewers made up of high court judge,bishop and recidivist housebreaker.
Just read history of gll, say that you prepared to leave your soul to them and you will be fine
Questions are standard
Very relaxed and in front of a panel of 3. Depending of role it could mean a presentation