The so-called "big four" accountancy firms are using knowledge gained from staff seconded to the Treasury to help wealthy clients avoid paying UK taxes, a report by the influential Commons public accounts committee says. Deloitte, Ernst & Young, KPMG and PricewaterhouseCoopers have provided the government with expert accountants to draw up tax laws. But the firms went on to advise multinationals and individuals on how to exploit loopholes around legislation they had helped to write, the public accounts committee (PAC) found. [includes company comments]