LONDON (Reuters) -British retailer Marks & Spencer's food business saw food sales increase 10.8% over the 12 weeks to May 17 year-on-year despite the fallout from a cyberattack last month denting availability, industry data showed on Thursday. Researcher NielsenIQ said M&S' share of the UK grocery market rose 20 basis points to 3.8% in the period year-on-year. M&S' sales growth did, however, slow from 14.7% in NielsenIQ's previous report.