Opening night at Tate Modern, 25 years ago this May, was the kind of party that defines an era. Stars of the arts world and politics, including prime minister Tony Blair, attended. All of them were dwarfed by a giant ­spider – Louise Bourgeois’s visiting sculpture – perched on the gangway over the vast, packed Turbine Hall. For Alex Beard, particular joyous moments still stand out, but not just from the evening: “It was a remarkable night, but I most clearly remember the first morning, 12 May, when I walked around outside, really early doors, and saw people lining up…