Very interesting. I just happened on your podcast. I'm one of those writers who toils away at his writing. Most of Ken Follett's routine is recognizable. I'll have a listen to the rest of the interviews.
Stumbled across your podcast and so happy I did. I’m not a writer (wish I had the imagination and discipline) but I do wonder how top writers go about it. I read Pillars of the earth years ago and it remains one of my favourite books. I learnt so much from it and I look at architecture in a different way. You asked all the questions I would have asked and Ken Follet gave such detailed answers it was so interesting and informative. Thank you, I shall be listening to more of your podcasts.
The word "key" here means "type", as in "type on a blank page". "Edit" here means "modify an existing page of text". So he is re-typing his whole manuscript by reading it off one screen/file and typing it into a new file. This way his brain processes every word through the act of typing, not just reading. In reading familiar material, it is easy to skim over and miss errors or awkward phrasing.