When I try following the Aeropress instructions (2 scoops coffee, fill to level 2, stir for 10 seconds, press for 20 seconds), I find that all the water has filtered through before I get to even 10 seconds of very gentle pressing. Most of the filtering takes place while I'm still stirring.
Am I doing something wrong?
I'm using pre-ground coffee (Tesco decaf).
It sounds as though the pre-ground coffee you are using is not ground fine enough. Generally the more coarse the grind, the faster water will filter through. You may try throwing some additional grind on your coffee, or buy pre-ground coffee that is more finely ground (although a snob such as myself would never actually advise buying pre-ground coffee).
The best solution is to turn the Aeropress upside down with the plunger already inserted into the barrel when you brew. This way, nothing drips out until you flip the whole thing over and start to press. The process is illustrated here. There are also lots of YouTube videos showing the method as well. With the assembly upside down like this you can let your coffee steep for as long as you want before extracting.
