Diamonds have funded wars in DR Congo, Sierra Leone and Liberia

Amnesty International and the campaign group Global Witness have issued guidelines, including questions people should ask retailers about the stones.

The proceeds of the illegal diamond trade have been used to fuel long-running conflicts in Africa.

A certification scheme was introduced in 2003 aimed at preventing the trade.

I don't believe people in Britain want this special gift to be related to the pain and suffering of others Tom Fyans Amnesty spokesman

The Kimberley Process requires governments to control imports and exports of rough diamonds.

But an Amnesty spokesman said there was still much to be done to end the illegal trade.

In a flashy brochure entitled "Are you looking for the perfect diamond?", the groups say as many as 22% of UK stores have no policy on conflict diamonds.

It urges customers to think about where the diamonds have come from.

"There's a lot to think about as you look for that special diamond," the brochure says.

THE KIMBERLEY PROCESS Established in 2002, it has 43 members including Sierra Leone, Democratic Republic of Congo and Angola It governs annual production worth $8.5bn and annual trade worth $20bn, 99% of the world's total output

"It's a once in a lifetime purchase, and you want to make sure your diamond is one that you and your loved one will cherish forever."

An Amnesty spokesman said he did not think consumers wanted presents which were essentially acts of love to be associated with killing.

"I don't believe people in Britain want this special gift to be related to the pain and suffering of others," the group's UK Economic Relations Manager Tom Fyans told Reuters news agency.

The guidelines include four questions which the groups say customers should ask when buying jewellery:

• Whether the jewellery contains diamonds

• Where the diamonds come from

• What the company's policy on conflict diamonds is

• Whether there is a written guarantee from suppliers.