Sainsbury’s, the supermarket group, is joining Marks & Spencer and Waitrose in targeting the food-on-the-move market. It will today unveil a standalone store in central London serving hot and cold food to go. The group, led by Justin King, has opened the site in Fleet Street on the edge of the City of London – near to the company’s own headquarters in Holborn and a few minutes from St Paul’s Cathedral. The store, which will open every week day at 7am, will compete with local competition such as McDonald’s, Pret A Manger and Chilango for the breakfast and lunch market. It is thought that Sainsbury’s will assess the performance of the pilot store before sanctioning a rollout of the concept. The group yesterday announced its “best ever” Christmas trading period