Property giant Land Securities made progress in its first quarter, but says the overall picture remains mixed with demand strong in some property types but weak in others.Total property sales in the quarter totalled £302.9m at 2.6% above March 2010 valuation and an average yield of 1.0%. Acquisitions were £174.6m at an average yield of 5.6%, with the O2 Centre, Finchley Road, in London and the Westgate Centre in Oxford accounting for most of that.In the investment portfolio, voids dipped to 5.7% from 5.9% while units in administration fell to 0.8%."There was good progress on lettings, success in selling properties into the areas of strongest investor demand, improvements to debt facilities from further treasury initiatives, progress on its London development pipeline and a start announced for the first large retail development in recent times at Trinity Leeds," chief executive Francis Salway said."We see strong investor demand in some sub-markets, but early evidence of price resistance in others. We will continue to play any such imbalances to our advantage," he added.