Persimmon has announced strong full year results, noting an “encouraging” start to 2012. For the year ending December 31 2011, the volume housebuilder’s pre-tax profit grew 55%, from £95.5 million in 2010 to £148.1 million. Its operating margin increased from 8.2% to 10%. Persimmon reported a healthy landbank, with 14,300 plots acquired over 2011. This brings the total of owned …