The mere facts of Westpac having a derivatives book, the sheer size of this portfolio and the material growth of derivatives at the bank provided scaffolding for ASIC agitation at the opening day of a trial over allegations of unconscionable conduct by the bank in the rates market.Philip Crutchfield, ASIC's counsel, took aim at Westpac's business model and risk management as he set up a narrative of systemic temptation to manipulate the daily bank bill swap rate setting mechanism to the profit of the bank."The BBSW was a key reference rate, and essential to the good operation of the [debt] market," Crutchfield explained, basics first, to Justice Jonathan Beach of the Federal Court at a hearing in Melbourne yesterday.Crutchfield soon turned simple facts into a motive for mischief."A feature of this case is the number of products that reference BBSW," he said."As derivative products and the like exponentially increased, as they became a bigger part of the book … and so Westpac was tempted to manipulate the rate, given their significance to the bank," Crutchfield told the court.Crutchfield framed a thin list of 16 occasions from 2010 to 2012 - the "alleged contraventions" by Westpac - as taking place during a period during which the Reserve Bank of Australia and the Australian Financial Markets Association had opened up a debate over practices in the bank bill swap market.AFMA's methods Crutchfield sniped at, noting of one rates committee report to the association's board: "the committees were strangely the actual traders."BBSW data sales, the ASIC counsel noted, accounted for 12 per cent of AFMA's revenue during the period of Westpac's alleged questionable conduct.The record on one AFMA BBSW committee meeting from May 2010 included the observation that "one of the many reasons for BBSW volatility is … the potential for prime bank panel members [including Westpac] to be able to influence rate sets to their advantage."Crutchfield told the court that "Westpac in very, very large part may drive and direct less liquidity [and is] able to manipulate the market."Queried by Justice Beach, Crutchfield said "it's enough to say they attempted to move the rate" with the ASIC advocate soon turning over bank emails "that show Westpac recognises the utility of the bank bill markets to manipulation."