I have had two years of failed "late" seed potatoes from Marshalls (who I think are brilliant seed merchants). Also the late carrots, late peas and late beans I sowed have failed. I think there may be some sales hype on the success rate of these late sowings which say "pick them right up to Christmas". I am in coastal Lancashire, soil is quite clay and damp.
are they grown in the ground I have had great success with Pots in buckets but have failed with overwintering Peas.
Good Luck