West End office rents are set to continue increasing, with investment yields across Central London softening by the end of Q4 2008, according to Knight Frank. The UK property advisor predicted that prime headline rents in the West End office market will increase by 5% to £115.50 per sq ft by end Q4 2008, and by a further 2% by end of 2009 to £118.00 per sq ft, securing it as the most expensive place to rent office space in the world. In the City, prime headline rents are forecast to remain unchanged at £63.50 per sq ft by end Q4 2008, and decline by 1.5% to £62.50 per sq ft by the end of 2009.