Plant specially prepared cold-stored tubers (available from specialist seed merchants) as home-saved tubers can suffer from pests and dormancy problems.

These late-planting (second-crop, like Maris Peer) varieties are, in fact, springtime seed potatoes. It is just that the tubers have been stored at low temperatures, so that when you receive them, there won't be a shoot on them.
They are usually posted out from early July to early August, so that they can be planted straight away in the warm summer soil without the need for chitting. This means that the potatoes will be ready for lifting from late October.

A similar propagation method - although it does involve chitting - is very easy to achieve at home. Simply leave some chitted seed potatoes from your January order in the seed tray where they are chitting, right through the summer, and plant them out on the last day of August.

Personally, I grow Pink Fir Apple (salad maincrop) which stays happily in the ground from March until December.

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