Online advertising spending in Britain surged 40.3% to 917.2 mln pounds ($1.72 bln) in the first half of 2006 compared to 2005, giving it a market share of 10.5%, IAB UK said. Internet is the fastest-growing advertising medium in the UK, commanding a market share of 10.5% for January to June 2006, up from 7.3% for the same period in 2005.