Just put loads of well-rotted compost on top of the soil now. You've probably just got time to let the worms take it down into the soil. If you want to grow potatoes go for main crop planted out end of March/April when risk of frost has passed.
I think a new veg patch does take about 3 years to reach optimum so be patient, but you will get a decent crop this year anyway. One other thing, if you plan to grow different types of veg you should really divide your patch up for crop rotation.