A majority of companies contacted replied in writing to the survey. However, the 11 who failed to respond are among the top 50 jewellery retailers in the UK by market share, with annual sales of more than £20m. Among them are Cartier, Graff Diamonds and Fraser Hart. John Lewis and House of Fraser also failed to provide any information on their diamond policy. Most companies were contacted four times. 

Since then the so-called Kimberley Process (KP), an agreement between governments, industry and non-governmental organisations, has sought to combat illicit trade and to prevent diamond smuggling from fuelling wars. The industry agreed to provide guarantees on the origin of all diamonds traded or sold to ensure they did not come from a conflict area.

Despite these pledges, “most top-selling UK jewellers still lack adequate policies to effectively combat the trade in conflict diamonds”, the report states.

“Most companies adhere to the industry’s minimal systems of self-regulation but these are not effective in preventing the trade in blood diamonds. A voluntary system will not bring the necessary change within the diamond industry.”

Conflict diamonds from West Africa “are still reaching the international market place”, and there are “credible reports of illegal diamond trafficking from Zimbabwe and Venezuela”.

Last year the publicity generated by the Oscar-nominated Hollywood movie Blood Diamond, which highlighted the link between civil conflict and diamond smuggling in West Africa, prompted the industry to launch a massive information campaign to educate retailers and prepare them to answer consumers’ questions about the issue.

The survey shows that awareness has increased: 96 per cent of respondents stated that they had adopted the KP-sanctioned system of warranties, the rules of self-regulation agreed to by the industry. Both the British Jewellers’ Association and the National Association of Goldsmiths encourage their members to seek a warranty as to the provenance of their diamonds, but few retailers were able to explain how the system was implemented. 

Only two companies, Tiffany & Co and Signet (including its subsidiaries Ernest Jones, H. Samuel and Leslie Davis) have taken stronger measures, commissioning rigorous internal and third-party auditing procedures to ensure the diamonds they buy are responsibly and ethically sourced.

The UK report follows a survey of the $33bn US jewellery industry, conducted earlier this year, which revealed a similar pattern. With a few notable exceptions, US retailers have no auditing procedures in place to combat conflict diamonds, despite the recommendation to do so by the trade association Jewellers of America.

KP members account for 99.8 per cent of all diamond production. As rough diamonds are a small, precious and easily smuggled commodity, some gems inevitably escape the net, but the KP has succeeded in imposing a regulatory system on the $60bn (£30.25bn, €44.6bn) a year industry.

The percentage of diamonds coming from conflict zones has dropped from 4 per cent to 0.2 per cent, although the end of several wars in Africa has contributed to this. But despite its achievements the KP is a slow-moving machine, hampered by its choice to use the carrot rather than the stick. The KP faced criticism last year for its slow response to the threat posed by the civil war in Ivory Coast.