You'll either find they don't need a spread at all like https://www.tesco.com/groceries/en-GB/products/253582556 - anything which has mayo on it means they get away without it. The "Just Ham" sandwich from Tesco does though, indeed, have butter.
That's just an arbitrary distinction to avoid calling things "margarine". Margarine had a bad reputation in the UK as something only poor people eat. In other places like the US it doesn't have this stigma and so people feel fine referring to it without euphemisms like "spread".
