SYDNEY, Sept 28 (Reuters) - Benchmark 10-year U.S. Treasury yields topped 4% on Wednesday as the ongoing collapse of British gilts shook confidence in bond markets globally, leading investors to demand fatter risk premiums. Persistent inflation has the U.S. Federal Reserve sounding ever more hawkish about interest rates - a view reinforced by relatively strong U.S. housing and confidence data overnight. On top of that, traders suspect Japan could sell Treasuries to fund its intervention in currency markets after it acted to stabilise a sinking yen last week.