Persimmon has reported strong half-year results, with its pre-tax profit rising 52%. Underlying pre-tax profit rose from £39.4 million for the six months to June 2011, to £59.7 million over the same period this year. Its underlying operating margin increased from 8% to 9%. Persimmon legally completed 4,439 new homes during the six month period against 4,657 last year. The …