- Rents continuing to rise- Low vacancy rates- Rental value expected to be at top range of estimatesFTSE-250 London based property firm Derwent London said rents are continuing to rise as demand reflects the improving economic outlook."The rental growth and strong demand we see for Derwent London's brand of space, together with the improving economic outlook, mean that we are confident that our portfolio's estimated rental value growth will be at the top end of the 4-6% range that we predicted for the year," said Chief Executive Officer John Burns.The European Public Real Estate Association (EPRA) vacancy rate, which is the estimated market rental value (ERV) of vacant space, fell to 1.2% from 2.4% in June 2013.Lettings in the second half to date totalled 121,200 square feet with an annual rent of £5.6m, up 11% from June's level."The first three quarters of this year have exceeded our positive expectations of last February. The UK's economic outlook has improved, with GDP growth of 1.9% in the first nine months of the year, and London continues to lead that recovery," the group added. Earlier this week Derwent completed the purchase of 19 Charterhouse Street, Clerkenwell EC1 for £39.25m before costs."Our successful refinancing means that we are now even better placed to fund our development pipeline and invest in additional properties." CJ