TO ME a galleria is a tunnel — as found on Italian roads, where notices remind drivers to accendiarise their lights in the galleria. To Ralph Halpern and Sir Terence Conran it is something far more magical: it is a retailing concept. Armed with the galleria concept and a couple of canvas-backed chairs and, now, with 53 per cent of Debenhams, they have undertaken to transform that stolid old business and its prospects and its profits. It is not easy to demonstrate the power of this concept in what is presumably its native land. A trudge round the dreary floors of Standa or Rinascente does not suggest that they have much to teach Debenhams, or even the Co-op. The market, though, is in a mood to accept such propositions, provided that they seem novel and glamorous and to do with retailing, which has succeeded elec- tronics, and oil exploration before that, as the market sector for marvellous tales. Now may be the time to remember that when such favourites fall out of fashion, they fall with a thump. Debenhams' out- going chairman Bob Thornton (who main- tained that he had always thought galleria to be the name of a disease) more than bore out City & Suburban's belief that he would sell his company's honour dearly. For him and for his shareholders there is light at the end of the galleria.