To make the sauce, cover the tomatoes with boiling water and leave for 1-2 minutes. Then peel, deseed and chop them.
Place them in a food processor with the stock, orange juice, wine, vinegar, sugar and pepper to taste, and blend until smooth. Alternatively, beat them by hand in a mixing bowl.
Transfer the mixture to a saucepan, bring it to the boil and cook rapidly for 5 minutes, or until reduced by half to a thick coating consistency. Whisk in the oil to make a glossy sauce, and keep it warm.
Cut away and discard the tough white muscle on each scallop and the coral, if attached. Lightly grease a ridged, iron grill pan or a nonstick frying pan with oil, and place it on a high heat.
When the oil is hot, add the scallops and sear them for 2 minutes, then turn and cook them for a further 30 seconds. Remove them from the pan and let them rest for 1 minute.
Pour the sauce onto two plates and divide the scallops between them. Garnish with basil leaves and serve.