With its traditional British red phone boxes, pubs serving fish-and-chips and tax-free shopping, Gibraltar has long drawn day-trippers from neighbouring Spain. But the easy flow of people across the border from Spain which underpins the economy of this tiny British territory on the southern tip of the Iberian Peninsula risks ending when Britain leaves the European Union's single market on December 31. Along Gibraltar's pedestrianised Main Street whose buildings feature decorative Portuguese tiles, Genoese shutters and British wrought-iron balconies, shopkeepers worry business will be hurt by tighter controls at what will be a new border between Britain and the EU.