It's the perfect time of year for a celebratory gin-and-tonic, and these days the tipple raised at Christmas may well have been made in London. After centuries of decline, the capital's distilling industry is picking up again, fuelled by small-scale producers and European rules changes that recognise 'London dry gin' as a distinct drinks category. Peter Day meets some of the entrepreneurs behind the trend and raises a glass or two to homegrown UK businesses.