Preheat the oven to 230C/475F/Gas 8.
For the roast pork and crackling, bring a kettle of water to the boil, suspend the pork on a metal rack over the sink or a bowl and pour the boiling water over the pork, discarding the water.
Pat the pork dry with kitchen paper, then rub all over with the olive oil and season, to taste, with the salt flakes and freshly ground black pepper. Roll the pork into a neat cylinder and tie with butchers' string.
Place the pork into a roasting tray and roast for 20 minutes.
Reduce the oven temperature to 180C/350F/Gas 4 and cook the pork for a further 1-1¼ hours, or until the crackling is crisp and the meat is tender and cooked through.
Remove from the oven, place the meat onto a plate and set aside to rest for 15 minutes.
Bring the juices in the roasting tin to a simmer over a medium heat.
Mix the softened butter and flour together until well combined and whisk into the juices, stirring constantly. Heat for a couple of minutes until the mixture has thickened slightly then season, to taste with salt and freshly ground black pepper.
Meanwhile, place the Bramley apples and water into a pan, cover and cook over a medium heat for 8-10 minutes, or until the apples have broken down and turned to a purée. Season with the caster sugar, to taste.
Meanwhile, for the fruity red cabbage, heat a large saucepan until hot, add the butter and red cabbage and fry for 1-2 minutes, or until just softened. Add the red wine, bring to the boil, then reduce the heat until the mixture is simmering and cook until the volume of liquid has reduced by half. Add the remaining ingredients and bring to a simmer, then cover and continue to cook for 40-45 minutes, stirring occasionally, until tender.
Remove the lid and cook for a further 5-8 minutes over a high heat, or until the liquid has evaporated and the red cabbage is slightly sticky and glossy. Season, to taste, with salt and freshly ground black pepper.
To serve, carve the pork into thick slices. Pile the red cabbage into the centre of each serving plate, top with a few slices of crackling-coated pork, spoon the pan juices around the edge of the plate and finish with a spoonful of apple purée.