Too much too soon

Somebody in the gym at lunchtime asked me if I was going running. I should have had the common sense and said "No" and walk away but stupid me says "I hadn't been planning to" and looked longingly at the empty treadmills. I then did the compulsive thing and leapt on one and run for a couple of miles (or 4) at a reasonable pace.

This in itself isn't bad until I count up the weekly miles. As part of my build-up I've been increasing my mileage by 2 or 3 miles a week. If I do my full long run tomorrow I will have increased it by 7 miles and be 4 miles over my target for the week. This is far too fast an increase and is likely to get me hurt. My legs actually feel a little tired at the moment. To compensate I'm planning to reduce the length of my long run tomorrow to make sure the mileage isn't too bad.