Europe's largest halal food company, Tahira Foods, has been forced to deal with emails and phone calls from concerned Muslim shoppers after an email smear campaign urged consumers to boycott the company.

Campaigner Abdul Raja, who last year gained attention when he urged Muslims to boycott all halal meat during July as a protest against what he saw as lax standards in the halal industry generally, said he emailed about 1,000 contacts, who in turn forwarded the email to many more.

He alleged the company's website misled consumers in claiming animals were slaughtered by a Muslim facing Mecca. An automated stunning and slaughtering line was used, he said.

Tahira Foods vigorously denied the allegations. MD Ghias El-Yafr said his company's website was accurate. Muslims were employed to carry out slaughter, he said, and while water baths were used to stun animals or "put them to sleep" before their throats were cut, this was allowed under certain halal cerification systems.

Slaughter methods are the subject of a fierce debate between different Muslim groups, with some scholars arguing the stunning of animals is allowed and others saying consciousness while the throat is slit is a prerequisite under Islamic law.

"It's been going on for 1,400 years," said El-Yafr. "Sharia is a wide spectrum. There is no one school of thought, and there are always some people who are more royalist than the king, and there are others who are far more liberal in their interpretation."

Raja said his campaign was not intended to stop the use of stunning, but to ensure the method used was declared on the label.

There is no central body for regulating halal standards in the UK; instead companies are verified by numerous halal bodies.

Tahira Foods supplies meat, fish, ready meals and prepared vegetables to the big four retailers, plus Somerfield, Budgens, Makro and Bestway.