I don't know Jamie Oliver's exact recipe, but it's pretty close to what I do. Nice variation: limes, and a few shots of tequila over the bird. Alcohol cooks off, but it's a nice savory note - my friend S calls it margarita chicken! I try to do one as close to once a week as possible -- economical, yummy, leftovers. Sandwiches. Cooked chicken to toss w/ veggies and pasta. Etc.

Also -- best way to avoid the "how long?" question? Get a digital thermometer with probe. Once you get the hang of where and how deep to put the probe, all your worries are over. No math, just wait until the therm beeps at 180 degrees. After a little mishap with G's first attempt at cooking a bird w/o me where we had the same problem as in your post, we're done with skipping on using the thermometer.