So, my attempt at eating 'what I want when I want' bombed massively. Who'd have thought it'd be so hard to follow your instincts? I ended up basically eating what I always eat and I was pretty sure of the calorie content of most of the things I ate. I even ate at the times I generally eat (according to a self-imposed 'eating schedule' that I've stuck to pretty much since I was 16 - 8 years). My single concession to the experiment, was a spontanious capaccino.
I have a theory that it was harder to be spontanious because I was at work, where I have quite a standard routine. So I'm going to try again on Friday, when I've taken the day off and have also planned to go to the cinema at the time I normally have my dinner, which should compel me to mix things up a bit. Fingers crossed I'll do better this time.