Claims of fraud and a disappointing trading update pushed UK banking stocks firmly lower on Thursday.Shares in Barclays plunged after a lawsuit was filed by the New York State Attorney General against the group's "dark pool" trading division. The complaint was made specifically in relation to its alternative trading system LX Liquidity Cross following an investigation by Attorney General Eric Schneiderman and alleges that it carried out fraud and "deceptive practices". The lawsuit is seeking unspecified monetary damages and injunctive relief, Barclays said in a brief statement. Barclays' stock was down nearly 8% at 211.75p by 14:32 after hitting a 52-week low of 209.4p earlier on.Michael Hewson, Chief Market Analyst at CMC Markets UK, said: "Not content with probes and fines into Libor, electricity trading, as well as an ongoing FX probe, we now have a probe into 'dark pools' in yet another blow to the banks and the industry's credibility.Meanwhile, Standard Chartered was also under selling pressure, down 4% at 1,205.82p, after its boss Peter Sands admitted that the emerging markets-focused bank experienced a "disappointing first half" with revenues and profits both below last year's.He said that the company faced difficult trading conditions across the global financial markets during the first six months of 2014, with revenues down by a "mid single-digit percentage" and operating profits 20% lower.HSBC and RBS were also trading in the red today, while Lloyds was bucking the trend, up 2%.Top performing sectors so far todayMobile Telecommunications 4,391.65 +2.20%Real Estate Investment & Services 2,635.94 +1.99%Chemicals 10,047.58 +1.92%Financial Services 7,995.72 +1.89%Automobiles & Parts 8,590.05 +1.66%Bottom performing sectors so far todayBanks 4,309.25 -1.60%Tobacco 39,529.67 -1.09%Technology Hardware & Equipment 1,055.48 -0.77%General Industrials 4,228.35 -0.41%Forestry & Paper 11,600.75 -0.37%BC