a mate at work has the same problem and bought these
http://www.screwfix.com/prods/18643/Drill-Bits/Specialist-Drill-Bits/Screw-Extractor-Set?cm_mmc=GoogleBase-_-Datafeed-_-Drill%20Bits-_-Screw%20Extractor%20Set
haven't tried them yet though, but looks promising
@kboy started
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a mate at work has the same problem and bought these
http://www.screwfix.com/prods/18643/Drill-Bits/Specialist-Drill-Bits/Screw-Extractor-Set?cm_mmc=GoogleBase-_-Datafeed-_-Drill%20Bits-_-Screw%20Extractor%20Set
haven't tried them yet though, but looks promising