In a half-year trading update, housebuilder Persimmon said interim revenues increased by 12% to £1.34bn, in line with expectations, thanks to selling prices and volumes boosted by post-election confidence and an increasingly competitive mortgage market.Volumes increased 7% to 6,855 units and the average selling price for the group increased by 4% to roughly £195,000, buoyed by factors such as continued supply contraints, growth in employment and improvements in disposable incomes.Total free net cash inflow before the £291m April capital return was £191m, up 56% on the same period the year before, swelling quidity cash holdings at the 30 June period end to circa £278m.The FTSE 100 group said its weekly rate of sale into the private market was 11% ahead of the prior year and that forward sales volumes were up 12% on last year at 4,606 new homes with an average selling price of around £213,000, 4% ahead of last year.Total group forward sales value at 30 June increased by 15% to £1.36bn.Despite suffering a slowdown in the planning application process in the run-up to the general election, Persimmon opened 122 new sites in the period to have 395 active sites at the period end, around 5% stronger than at the start of the year.More than 11,000 new plots of land were added to the land bank across the UK, taking total to roughly 92,400 plots.