Light the barbecue. Meanwhile, put the butter, olive oil, garlic, chilli, paprika and sherry in a small pan set over a high heat. Season well and bubble for 2 mins.

Put a square 45cm sheet of foil shiny-side down on a work surface. Lay an equal-sized sheet of baking parchment on top, then fold the foil and parchment in half together, with the foil on the outer side. Seal at the shorter sides by folding the edges over a few times and pressing them firmly. Spoon the prawns into the parcel through the open top and pour in the melted butter mixture. Fold the parcel edges together along the open top to seal it fully.

When the coals of the barbecue are ashen, place the parcel directly on the grill and cook for 15 mins, carefully turning it once or twice. The prawns will be nearly ready when the parcel begins to puff up with steam. Remove the parcel from the barbecue, open it up carefully and tip the prawns and buttery juices into a serving bowl. Squeeze over one of the lemon halves and sprinkle with the parsley. Cut the remaining lemon half into wedges. Serve the prawns with the lemon wedges for squeezing over and crusty bread on the side for mopping up the juices.