Land Securities said interest in London's "Walkie-Talkie" building and other developments had increased and that the rest of its properties were virtually full.Britain's biggest commercial property company said 20 Fenchurch Street, known informally as the "Walkie-Talkie", was 52% pre-let with another 4.0% in solicitors' hands.In total, the company completed £5.5m of development lettings in the three months since April 1st with another £12.3m in solicitors' hands, Land Securities said in a trading statement.Land Securities has invested heavily in the London market, arguing that there is not enough high-quality commercial property for tenants' needs. The capital's economy is picking up amid wider signs of strengthening UK economic growth.In retail, units in administration fell slightly to 2.2% from 2.3% despite the failure of chains such as Dwell, Modelzone and Ortak. Total retail sales were up 2.5% by letting empty units and bringing in stronger retailers.Chief Executive Robert Noel said: "In London, demand is increasing and we remain confident that our portfolio is well positioned and our developments well timed. Overall, the retail market remains challenging but we are maintaining very high levels of occupancy in our centres and are pleased with our increased exposure to leisure."