Food and drug retailers fell by an average 12% on Thursday as a number of trading updates and results failed to impress.Supermarket titan Tesco led the declines falling nearly 15%. 'Must do better' is the theme of the firm's Christmas trading statement, as it saw the sales performance in its home market fall below expectations, prompting the company to advise full-year trading profit growth will be around the low end of the range of analysts' expectations.Sales excluding fuel but including Value Added Tax (VAT) in the six weeks to January 7th were down 1.3% on a like-for-like (LFL) basis versus the previous year.Blue chip peers Morrison and Sainsbury were also feeling the pressure, trading around 6% down each in the afternoon period.FTSE 250 cash and carry operator Booker fell over 3% despite saying that LFL sales rose 6.7% in the 16 weeks to December 30th from the corresponding period of 2010, with customer numbers and average spend per customer both up year-on-year.Shares in chocolate retailer Thorntons dropped nearly 30% after it reported a weaker-than-expected 0.6% rise in total sales over the important Christmas trading period. In the 14 weeks up to and including 7 January 2012 total sales increased to £83.7m as it battled against tough retail conditions.The sector was the worst performing category of the day, even though online grocer Ocado surged over 30%. The firm said it enjoyed a festive surge with gross sales in the seven trading days to Christmas rising 23.8% from the same period in 2010. Meanwhile, the best performing sector today was industrial metals and mining with FTSE 250 firm Ferrexpo doing its bit to provide a lift.The Switzerland-based, but Ukrainian-owned, iron ore producer increased total pellet production by 3.3% in the fourth quarter of 2011 compared to the previous three month period. Pellet production from its own ore during the whole of 2011 was in line with 2010, with both years at full capacity.BCTop performing sectors so far todayIndustrial Metals & Mining 4,464.82 +2.22%Financial Services 4,423.52 +2.14%Insurance (non-life) 1,371.23 +1.61%Life Insurance 4,028.35 +1.53%Chemicals 7,178.81 +1.45%Bottom performing sectors so far todayFood & Drug Retailers 3,963.37 -11.98%Electricity 7,976.36 -1.17%General Retailers 1,506.87 -1.03%Aerospace and Defence 3,459.91 -0.97%Health Care Equipment & Services 3,393.61 -0.68%