It's that time of year again. Promenaders will be donning their finery and flocking to events around the country to celebrate the highlight of the classical music season. Stephanie Andrews introduces the opening concert live from the Royal Albert Hall , where chief conductor Leonard Slatkin will be leading the BBC Symphony Orchestra and BBC National Chorus of Wales with mezzo Irina Tchistyakova and baritone James Rutherford in tonight's programme.