Investors are turning their back on the use of currencies benchmarks amid a global probe into possible manipulation of foreign-exchange markets, attendees at an industry committee said.

At the meeting of financial-markets association ACI in London on Wednesday, banks and investors said the volume of transactions traded at so-called "fixes" had fallen off sharply, according to several people who attended the event. The benchmark that is measured from trades executed around 4 pm in London each weekday, which has been at the center of a global probe that began in the UK last April, is particularly falling out of favour.