The advocacy organisation has gone through the supply chains of 13 big jewellery makers and found big gaps between company sourcing policies and practices.

HRW ranked Boodles, Chopard, Christ, and Harry Winston as ‘weak' in responsible sourcing and Tanishq was ‘very weak'. Companies were judged on making sure their precious metal and stone suppliers were not buying from artisanal mines with child labour or other exploitative labour practices.

The best-ranked out of the companies was Tiffany & Co, which HRW said could track its gold right back to an individual mine, with Chopard and Cartier also commended for their links to producers.

Rolex and two other companies refused to tell HRW anything about their supply chains.

Juliane Kippenberg from HRW said jewellers needed to make more of an effort.

"Many jewellers can do more to find out if their gold or diamonds are tainted by child labour or other human rights abuses," she said.

"When someone buys a piece of jewellery for their loved one this Valentine's Day, they should ask their jeweller what they have done to find out about its origin."

HRW said Boodle and Christ had pledged to do better after being questioned on their supply chains.