By James Davey LONDON (Reuters) – Tesco, Britain’s biggest retailer and one of the country’s largest private sector employers, is facing union calls to increase store workers’ pay after several rivals raised hourly rates for a second time this year. Competition to attract and retain staff is heating up in a tight UK labour market amid a worsening cost of living crisis. Sainsbury’s, the country’s second largest supermarket group, Marks & Spencer and German-owned discounter Lidl GB have all announced increases this month, paying hourly rates ahead of the market leader. Tesco, which has a UK work…