Bring a pan of salted water to the boil. Cook the potato for 8-10 minutes or until tender.
Meanwhile, heat the oil in a non-stick frying pan and cook the sausages for 10-12 minutes, or until cooked through, turning frequently.
Drain the potatoes and return to the pan. Mash with the cream and butter until smooth. Stir in the chives.
For the sauce, blend the blackberries, red wine and stock in a mini-food processor until smooth. Transfer to a pan and reduce until thickened.
To serve, transfer the sausages and mash to a serving plate. Drizzle the sauce over to serve.