Be prepared for a large surprise on the Thames River at Nine Elms this September.   What surprise exactly?  Well Dutch artist Florentijn Hofman is preparing his first UK commission.  This will be semi-immersed in the Thames, and will rise and fall with the tide.   Almost certainly it will be large.  Very large.  It is closely under wraps until 2 September, when it will be transported along the Thames, and is likely to be a talking point in the up and coming Vaxhall area.  Hofman is famous for large scaled up sculptures of everyday objects.  Not surprisingly his 26-metre high inflatable “Rubber Duck” has been the focus of much attention in a variety of cities, including Auckland, Sao Paolo and Osaka.