LONDON — The Real Bread Campaign in the United Kingdom is calling for a legal definition of sourdough bread and making consumers aware of what it calls “sourfaux.”

Sourdough bread is leavened using only a live sourdough starter culture, according to the campaign. The term sourfaux refers to bread named or marketed using the word sourdough but manufactured by a different process that uses baker’s yeast, chemical-raising agents, additives or a combination of the three items. Some of the so-called sourfaux products are being sold for at least twice the price of comparable products from the same brand, according to the campaign.

The campaign has created an honest crust act that asks local members of parliament to urge the government to create legal definitions for a range of common bakery marketing terms, including sourdough. The act also seeks full ingredient labeling on unwrapped bread loaves.

More than 150 bakery professionals in the United Kingdom signed a letter that the campaign on Aug. 16 sent to George Eustice, the secretary of state for Environment, Food and Rural Affairs. The letter urges the government to include the honest crust act proposals for comment in public consultation in a review of bread composition, labeling and marketing regulations.

“How can companies justify charging premium prices for products manufactured by standard processes?” said Chris Young, coordinator for the Real Bread Campaign. “Why is more not being done to protect shoppers? Someone trying to pass off vodka with a drop of scotch in it as single malt whisky would be stopped. Why is this sourfaux free-for-all being allowed to continue?”