(ShareCast News) - Derwent London reported a 5% increase in first-half net rental income and a 22% rise in pre-tax profit, as it said office demand was "voracious".Net rental income rose to £66.9m from £63.7m in the six months to June 2014, while EPRA profit came in at £39m from £32m. The interim dividend was lifted 8.2% to 12.60p.Net profit attributable to equity shareholders rose to £397.2m from £365.0m.Chairman Robert Rayne said: "We believe that 2015 will continue to be a very good year for Derwent London based on strong occupational demand, the quality of our product, our clear-cut strategy and our effective financing."The company said it remains confident in it markets and raised its average portfolio ERV growth estimates for the full year to 8-10%, saying it expects property yields to remain firm in the second half.So far in 2015, £20m of new lettings have been secured and the company said it has the potential to deliver over 1m square feet of developments between 2016 and 2019.