Par boil them for 10 minutes, drain and then tip them back into the pan. Put the lid on and shake the pan vigorously. This is to rough up the outsides of the potatoes a little, which will help to get them to absorb the fat which makes the outsides lovely and crunchy.
Put your roasting tin on the hob and pour a generous amount of oil into it - you're looking for a good coating on the bottom, about 1mm. Thisisimportant.
Heat the oil till it's really hot and then tip in the potatoes. Spoon hot oil over the top of the potatoes, or turn them all so that they're coating in fat, then put them into a hot oven (around 230 I think?) and cook for around 40 minutes. Check them after 20 minutes and turn them so that they brown all over.
When cooked, serve immediately. Don't try and keep them warm as they will go soggy.
NB - the chicken is probably on a lower temperature than the oven will need to be. This is fine. The chicken can come out of the oven about 30 minutes before the potatoes are ready, and if you cover it with foil it will stay hot enough to serve. Will also benefit the chicken as the fibres relax and the meat is actually more tender when you serve it.