By David Milliken LONDON (Reuters) – British retailers reported lacklustre sales around Christmas, according to industry data released on Tuesday which may add to concerns that the economy has tipped into a mild recession, less than a year before a likely national election. The British Retail Consortium (BRC), a trade body for supermarkets and other big stores, said spending in cash terms in December was 1.7% higher than a year earlier, representing a fall in purchases after inflation is taken into account. “The festive period failed to make amends for a challenging year of sluggish retail sal…