Put the tomatoes into a heatproof bowl and just cover with freshly boiled water. Leave to stand for 1–2 minutes until the skins start to split. Carefully pour off the hot water and peel away the skins. Roughly chop the tomatoes on a chopping board.
Heat the oil in a medium, heavy-based saucepan for 1 minute. Add the onion and celery and fry gently for 5 minutes, stirring until just beginning to colour.
Tip in the beans, tomatoes, mustard, treacle, ketchup and Worcestershire sauce and stir the ingredients together. Heat until the liquid starts to bubble around the edges. Reduce the heat to its lowest setting and cover the pan with a lid. Cook gently for about 10 minutes until the tomatoes have softened to make a sauce.
Serve with toast or on jacket potatoes.