What it is
E471 is a mix of mono- and diglycerides made by reacting glycerol with fatty acids. The fatty acids can come from vegetable oils (palm, soybean, sunflower) or animal fats (tallow, lard). In the EU and UK, palm-derived is the most common source today.
Why it matters
Extremely widespread emulsifier — bread, pastries, ice cream, margarine, peanut butter, ready meals, chocolate. Often the "secret ingredient" that gives industrial baked goods their texture.
What to do
Variable. Most major UK food brands now use plant-derived E471 (palm or soya) and will confirm if asked. For premium, artisanal, or non-EU products, animal-derived is still common and a direct question to the manufacturer is the only reliable check.