I par-boil my spuds, toss them in the strainer to make them fluffy, throw in some herbs, toss some more. Then I take the roast out to rest (usually under foil in the grill area of the oven - to keep warm) and then put the spuds into the pan, I usually have par-boiled a piece or two of sweet potato and also throw in a few cloves of garlic, I turn the heat up in the oven and cook the veges for 10-15 mins to make them crispy since they don't have to cook.

While this is going on I steam the other veges that we're eating. They're all then ready about the same time.