Tangled typing: finding out the plot as you write

I am, like many people, a creature of habit. At the moment I'm in the habit of writing each lunchtime at work and until something disrupts it and I fall into a new lunchtime habit, it's working well. Either discipline, or not wanting to have to think of what to work on next, is causing me to stick to stories longer than I often would; instead of moving on at the first difficult decision, I'm having to choose a path and work my way down it. You might think that's leading me into the realms of properly planned plots, but interestingly it doesn't seem to be.

This week I've come back to a story I started a year ago (at least) and have written the odd paragraph of since but never got to grips with. It began from a 5-minute free-writing exercise sparked off by a woman I passed in the street, having finished reading a Dashiel Hammett novel the night before. Now it seems to be a sort of detective story in a future dystopia, with a life of its own. I can only imagine my subconscious is working away on the plot while I manipulate data at the dayjob, or maybe I'm dreaming my way through the difficult parts; yesterday they found a clue and I was so excited, because I would never have thought of looking behind the cushions in the waiting room. Except, hang on, wasn't it me that thought of making them do that?

Sometimes I read advice from other writers and I feel like I should sit down at the start of every story with a clipboard and pen, interview the characters and draw a route-map. Every now and then I try it. Once in a while it even works, but I was a reader before I was a writer and I want the thrill of discovery, I want the twists and turns, the ups and downs. I want to be wrong-footed and fall for a couple of red herrings. Somehow my disorganised, chaotic brain lets me do that while I write, and yes I might have to tie up a few loose ends in the redraft, but don't most people? Give me untidy and enjoyable over planned and methodical any day. At least I'm following that other standard piece of advice by having a regular writing routine.