- Sees seven per cent portfolio rental growth in 2014- Vacancy rate remains low- Momentum continues in a strong marketFTSE 250 property firm Derwent London sees up to seven per cent portfolio rental growth in 2014 as momentum continues in a strong market.The group, which rents out offices in London, reiterated its full-year guidance for portfolio rental value growth of around 5% to 7% and for property yields to remain firm.The group reported lettings of 57,500 square foot for £2.4m pa in the first quarter, with comparable lettings 5.2% ahead of December 2013.EPRA vacancy rate, a key performance measure in real estate, remains low at 0.9%.Derwent has made £13m of acquisitions and £38m of disposals in the year to date and had undrawn facilities of £390m at the end of April.Chief Executive Officer John Burns commented: "We continue to experience deep demand for Derwent London's brand of space. This gives us the confidence to drive our extensive development programme forward and to reiterate our 2014 guidance for portfolio rental value growth of around 5% to 7% and for property yields to remain firm."CJ