Underlying profit at Persimmon hit £7 million last year as the firm announced strong forward sales and plans to open 90 new sites in the first half of 2010. Persimmon reported pre-tax profit of £77.8 million but this includes a £74.8 million writeback of land value. The firm completed 8,976 units in the year, down from 10,202 in 2008. But …