Using a pestle and mortar, bash and bruise the bay, rosemary and thyme with the garlic, olive oil and 1 tbsp of the vinegar, plus some seasoning. Smear the mixture all over the meat to marinate. Can be done up to 24 hrs ahead.
Set aside the fennel fronds and sliced spring onions, and toss the rest of the vegetables in 1 tbsp of the olive oil and some seasoning. Build your barbecue so that there is a higher pile of coals on one side and a lower pile on the other. Light the barbecue and, when the coals are ashen, grill the vegetables (be careful that the asparagus and spring onions do not fall through the bars) until lightly charred and wilted. Scoop them into a dish and dress with the rest of the olive oil and the lemon juice, then scatter with the fennel fronds and sliced spring onions, and set aside.
Now cook the pork. It needs to sizzle for 1 hr over a fairly low heat – the coals should be grey but, to ensure they don’t go out halfway through cooking, you may need to keep adding occasional coals. Lay the pork on the coolest side of the barbecue, fat-side down, and brown for about 20 mins until well charred (if you have a kettle barbecue, cover with the lid). Use tongs to flip the meat and continue to cook slowly for about 1 hr more, turning and moving the meat occasionally, until the thickest part is very firm when prodded, or when the juices show no sign of pink when pierced with a skewer. If you have a digital cooking thermometer, it should read 65C or more when inserted in the thickest part. (If the pork is organic, it’s fine if it’s a tiny bit pink, but you certainly don’t want it raw.)
When the pork is cooked, place on a dish, scatter with parsley, drizzle over the rest of the vinegar and leave to rest somewhere warm for 15 mins. Carve the pork into thin slices on a board and serve with the just warm vegetables and vinegary resting juices.