Heat the oil in a large ovenproof pan and fry the meat over high heat until browned all over. Remove with a slotted spoon and set aside.
Preheat the oven to 160C/140C Fan/Gas 3.
Add the butter and leeks to the unwashed pan, and fry for a few minutes. Sprinkle in the ginger, paprika and flour, stir and cook for a minute. Stir in the stock and bring to the boil, stirring until thickened. Add Worcestershire sauce and season with salt and pepper. Return the meat to the pan, bring to the boil, cover with a lid and simmer for a few minutes.
Transfer to the oven and cook for about 1¾–2 hours. After this time, stir in the celeriac, bring back to the boil for a few minutes then return to the oven for about 30 minutes, until the meat and celeriac are tender.
Stir in the horseradish cream, sprinkle with parsley and serve at once.