Land Securities will start £655m of development projects in London this year to take advantage of expected 'good rental growth' in the West End office market.In a third quarter trading update, it said it's in the process of placing construction contracts on three major developments.Building at the £415m Park House project in Mayfair will begin in May, providing 165,000 sq ft of offices, 90,000 sq ft of retail and 60,000 sq ft of residential space. The Selborne House scheme in Victoria Street, SW1 will provide 250,000 sq ft of office accommodation, plus street-level shops and restaurants. A start date for the £185m project is being finalised, but should finish in 2013.Making up the trio is Wellington House, Buckingham Gate, SW1, a residential development of 60,000 sq ft providing 59 units. It'll cost £55m and deliver in mid-2012.Also today, the company said lettings increased by £9.8m during the third quarter, with another £22.6m currently in solicitors' hands. Lettings for the year-to-date are £39.7m.There was only one investment property sale within the London portfolio during the period, bringing to an end the firm's recent programme of disposals. 'Disposals in the near term are likely to be limited and undertaken for capital rotation and portfolio management reasons,' it said. Within the retail portfolio, the void level on its like-for-like properties rose to 5.2% at the end of December from 4.8% in September. Group LTV (loan to value) at 31 December 2009, based on 30 September 2009 asset values, was 49.1% versus 50.8% at the end of September.'The business continues to perform well against our operational targets and we are pleased that our portfolio is proving its appeal to occupiers with ongoing lettings, while our financial strength allows us to be first off the block with our London development programme,' said chief executive Francis Salway.The third interim dividend payment for the current financial year will be 7p a share.