Property group Derwent London saw the underlying value of its property portfolio increase by 5.1% in the first six months of 2011, a benchmark-beating performance. Over the same period, the Investment Property Databank (IPD) Capital Growth Index for central London offices grew 4.6%.Adjusted net asset value (NAV) per share on an EPRA (European Public Real Estate Association) basis rose by 10.0% in the first half of the year to £16.21p from the year-end figure of £14.74.EPRA profit before tax edged up to £26.6m from £26.3m last year, while statutory profit before tax, which includes valuation movements, was £173.3m compared to £214.1m in the first half of 2010. The year-on-year reduction in statutory profit was primarily caused by a reduced revaluation surplus this time round; the 2011 revaluation surplus was £117.3m, versus £197.5m in the first half of 2010.Net property income climbed to £57.8m from a restated £54.9m last year.Lettings completed in the year to date together with space put under offer have reduced the level of immediately available space to only 1.1% and, overall, the open market lettings made in the same period achieved rents 10.1% above the December 2010 estimated rental values, the company said.As at 30 June 2011, the group's net debt had increased to £904.5m from £887.8m at the year end. However, with the increase in property values over the period, the group's loan to value ratio declined from 35.7% at 31 December 2010 to 34.2% at the half year."Although the economic outlook has become more uncertain in recent weeks, the group is well positioned with its substantial reversionary income stream and flexible pipeline of future schemes," said John Burns, Derwent's chief executive.The interim dividend has been increased by 8.0% to 9.45p per share from 8.75p at the interim stage last year.The share price rose 12p to 1,567p in early trading on the morning of the results announcement. --jh