Paint & Paper Library is a decent choice if you want low odour and low emissions without going full eco-purist. Its core interior finishes are water-based and fall into the low-VOC bracket, which means minimal smell and faster recoat times — the kind of paint you can sleep in the same room as the night after decorating. That's a world away from old solvent-heavy trim paints.
Where it lands honestly: it's a quality British paint brand with good pigment density and a lovely tonal range — Slate IV, Lead II and the softer Paper III are proper grown-up colours — but it doesn't lead with eco credentials as a headline. The formulations are modern and compliant, not plant-based or mineral. So calling it "eco-friendly" is fair on VOCs and water-based chemistry, but it's not making the claims a specialist green brand makes.
If eco performance is genuinely top of your list, Earthborn and Edward Bulmer are the two to look at. Earthborn's clay-based emulsions are breathable, virtually VOC-free and brilliant for older lime-plastered walls that need to breathe. Edward Bulmer goes further with natural, plant- and mineral-based paints — about as low-impact as it gets while still giving you a serious decorator's finish.
The honest middle position: Little Greene and Farrow & Ball are both water-based and low-VOC across most of their interior range too, so you're not sacrificing eco credentials by choosing any of the premium British brands. They're all in the same broad bracket.
My practical advice — don't choose paint on the eco label alone. The greenest paint is the one you only have to apply twice instead of four times. Paint & Paper Library covers well and lasts, which counts for a lot environmentally. If you want a breathable finish for period plaster, go Earthborn. If you want the lowest impact going, Edward Bulmer. Otherwise Paint & Paper Library is a sound, low-odour choice you won't regret.