LONDON (AFP) - London's underground train service was virtually halted by a strike over pay on Monday, disrupting the start of the post-Christmas sales and sporting fixtures. Most lines were shut or operating a vastly reduced service, with people forced to use buses or taxis to reach shops which are desperate for business after disappointing sales in recent months. Members of the London Underground train drivers' union ASLEF voted overwhelmingly to hold a 24-hour strike on December 26, a public holiday in Britain known as Boxing Day, and on three more dates in the coming weeks. Drivers are angry that their employer is refusing to give them extra pay and a day off for working on Boxing Day.