Persistent concerns over Greece defaulting on its sovereign debt obligations and heightened UK political risk dented market confidence as the FTSE 100 slipped below the 7,000 mark and firmly into the red.At 15:14 BST on Friday, the blue chip index was trading down 1.02%, or 71.83 points, at 6,988.62 with consumer and food related stocks along with natural resources, engineers and insurance sector bearing the brunt of the sell-off.Already bearish sentiment was compounded when Fitch Ratings joined others in the City to flag up political risk for utilities, rail operators and housebuilders, as the UK seems on course for a hung parliament after the general election on May 7.With the Conservatives and Labour having promised price freezes for rail fares and utilities prices respectively, Fitch flagged up both sectors as being particularly vulnerable to policy or regulatory risk, while stressing there was no immediate credit ratings risk just yet.Overall, during a trading session where hardly any sector traded in the green, industrial metals and mining stocks bore the brunt, with the segment's headline index down 5.99% or 121.14 points at 1,901.79.While base metals got some respite, concerns about the wider mining landscape and the ongoing iron ore market slump weighed heavily on investor sentiment.Evraz (down 6.96%), Kaz Minerals (down 5.13%), Vedanta (down 4.79%), Anglo American (down 3.18%), Antofagasta (down 2.14%), Glencore (down 1.75%) and Rio Tinto (down 1.72%) typified Friday's bearish session, with Lonmin (up 0.95%) among the few in the sector to buck the sector trend.Tesco (down 2.22%) led food and drug retailers lower, while a plethora of life insurance stocks - Prudential (down 1.74%), Old Mutual (down 1.54%), Standard Life (down 1.41%), Aviva (down 1.36) and Legal & General (down 1.21%) - took a battering as Bloomberg data terminal outages hit the market during the morning's trading session.BP (up 0.74%), Whitbread (up 0.19%), Experian (up 0.17%) and Rolls-Royce (up 0.10%) were among a handful of cross-sector stocks that just about managed to stay in the green during a largely negative session dragged lower by macroeconomic malaise. Rolls-Royce in particular benefitted from a record £6bn order for aircraft engines thereby keep its share price in the green on a rocky Friday.Worst Five Sectors:Industrial Metals & Mining 1,901.79 -121.14 -5.99%Food & Drug Retailers 8,477.83 -187.04 -2.16%Mining 13,844.75 -243.18 -1.73%Industrial Engineering 9,329 -149.87 -1.58%Life Insurance 8,471.96 -119.39 -1.39%