Land Securities said rental values in London are rising due to a shortage of new commercial spaces.In the third quarter the group signed £10.9m investment lettings, according to a trading update on Wednesday.Retail sales were up 3.2% like-for-like during the quarter.The group made portfolio sales of £701.6m on the back of £234.6m of acquisitions including a 50% stake in Thomas More Square, in East LondonDuring the period the company completed and sold a number of shopping centres in the UK."Interest in our developments is strong and on terms ahead of our valuers' most recent estimates," said chief executive Robert Noel."Although there is political uncertainty at home and abroad, we expect interest in our schemes to remain strong, reflecting both the quality of our portfolio and the lack of supply in London."