LONDON (AFP) - Religious leaders in Britain on Thursday called for all meat to be labelled with details of the method of slaughter after it emerged halal and kosher meat in supermarkets is often not marked as such.

Representatives of Jewish and Muslim groups said in a letter to the Daily Telegraph that consumers should be informed at the point of sale of precisely how animals have been killed.

The call for comprehensive labelling comes after it emerged that people eating at Pizza Express and other restaurants were eating halal-slaughtered chicken without their knowledge.

"Comprehensive labelling should be supported by faith communities and animal welfare groups alike," said the letter signed by Henry Grunwald, chairman of Shechita UK, the body which represents the Jewish method of religious slaughter, and Dr Shuja Shafi, Deputy Secretary General of the Muslim Council of Britain.

Food labels should specify whether or not an animal has been stunned prior to slaughter "and whether it has endured repeat stuns if the first attempt was ineffective," they added.

"They should also be told the method of slaughter: captive bolt shooting, gassing, electrocution, drowning, trapping, clubbing or any of the other approved methods," the letter said.

More than 70 percent of New Zealand lamb sold in Britain now comes from halal slaughterhouses, although there is currently no requirement for that information to be stated on the packaging.

Halal methods are used to ensure the meat can be sold to both Muslim and non-Muslim nations, with Middle East countries a major market for New Zealand lamb exports.

"We all follow the rules set down by the European Union (in the British market)," Craig Finch, UK and Europe Regional Manager for Beef and Lamb New Zealand told AFP.

"Currently there is no labelling requirement in terms of halal.

"It's based on commercial and logistical factors - we take a consistent approach that meets regulations across the board in our different markets around the world." Asked whether clearer labelling should be considered in Britain, Finch said that it was a matter for regulators in different markets and that limits should be placed on labelling because of space constraints.

"It really becomes a regulatory issue. But that information about slaughter methods is already clear on our website," he said.

Finch added that all of the lamb exported to Britain was from sheep that had been "pre-stunned" and was unconscious before slaughter in accordance with New Zealand law.