The inquiry resulted in three changes to police procedure, however: firstly, that anyone interrogated should be told beforehand about the possible consequences and purpose of the statement; secondly, that the statement should normally be taken at home; and thirdly, that in cases "involving matters intimately affecting [a woman's] morals" another woman should always be present for any interviews. United Diamond Fields v Joel Hastings was next involved in United Diamond Fields of British Guiana Ltd v Joel and Others, which he considered both his most difficult and most interesting case. Following the discovery of the diamond mines in South Africa, men such as Solly Joel had established a diamond syndicate to restrict the amount of diamonds on the market. For this to work, they had to control the entire output of diamonds in the world, which they planned to do by acquiring interests in all of the diamond mines. In 1925, British Guiana began producing enough diamonds to attract the attention of the syndicate, and in November 1925 a Mr Oppenheimer, representing the syndicate, entered into a contract with Mr Perez, the operator of the Guiana mines, to have worth of diamonds provided to the syndicate over a twelve-month period. A few months later, United Diamond Fields of British Guiana was incorporated as a limited company. The company used Oppenheimer as a technical adviser, and immediately arranged to have its diamonds sold to the syndicate. The price was to be fixed for six months, with an auditor's certificate at the end of that time used to negotiate a new price. Oppenheimer was the only one with access to the accounting information, and the rest of the company had no way of checking that his figures were correct. In the same time frame, a new deposit of diamonds was discovered in South Africa, forcing the syndicate to acquire several million pounds worth of these new diamonds to prevent their control over the market being destroyed. This strained their finances and the new diamonds forced the price down. To correct this, the syndicate were forced to reduce the flow of diamonds from British Guiana, which they did by getting Oppenheimer to reduce the price of Guianan diamonds to the point where the company output dropped from a month to less than per month. Oppenheimer then claimed that the profits were only five percent, forcing the company to reduce the price yet again.