Thanks for the reply GB, it was more the level of detail they expect on the form you fill in I was after.
The form itself does not require much detail. From what I remember you merely need to outline the event without going into the specifics. Just a couple of sentences about what the situation was, and then an overview of what action you took.
eg
"A flash fire broke out in a neighbour's house caused by a gas cooker. I told a bystander to call the emergency services before attempting to locate the shut off valve outside the house and calling on all the neighbours doors and telling them to move to a safe area. When the emergency services arrived I told them what action I had taken."
(not a real incident - I just made that up but it's about as much detail as would be required)
The detail comes in the interview itself. The important part is to read the question carefully and ensure you don't start writing things that have not been asked for. Also, I don't believe you are assessed on hand writing per se, but if the assessor can't read it then you've got problems, so take your time.
Have fun!