Clean the venison by cutting away any tendon. Leave on the silver skin as this will cook down. Cut the venison into 6 cm (2½ inch) cubes.
Increase the heat to high and add the remaining oil. Lightly season the venison and cook, in batches, for 3–4 minutes on all sides until browned.
Add the sherry and red wine, scraping up any cooked-on bits from the bottom of the pan. Return the meat and vegetables to the pan with enough water to cover the meat and bring to the boil. Reduce the heat to low and simmer gently for 2 hours, skimming off any foamy residue that rises to the surface. Add
Remove the cooked venison, cover with foil and keep warm. Reduce the sauce until it has a light, coating consistency by cooking over high heat for 15 minutes. Season to taste.
To serve, strain the sauce through a fine sieve, place the meat on a plate and spoon the sauce over the meat.