Reach for Dulux Snow Scene — it's the nearest Dulux colour to Little Greene Loft White, measuring ΔE 2.3 from the original. Anything under 2.5 is what we'd call very close: you'd struggle to tell them apart on a wall, and once the light shifts through the day the gap all but vanishes.
Snow Scene sits at LRV 90.3, so it's a genuinely bright, soft white that bounces plenty of light around. That's the whole appeal of Loft White — it's a clean, airy off-white without the cold blue edge you get in a lot of brilliant whites. Snow Scene holds onto that same gentle warmth.
If you can't get Snow Scene, Dulux Absolute White is your backup at ΔE 2.5 and LRV 91.3. A touch brighter and a hair further from the original, but still well within striking distance. I'd only go for it if Snow Scene isn't easy to lay your hands on.
Now the honest bit, mate: a ΔE 2.3 match is close, but it isn't a clone. Little Greene whites carry their own depth and pigment quality that a colour-match in a different brand's base won't replicate exactly — particularly in low north-facing light, where subtle whites show their true character. If you're matching into an existing Loft White room and the difference will sit side by side on the same wall, that small gap can catch the eye.
So here's the practical steer. If the whole room is going to be repainted, Snow Scene will do the job beautifully and nobody will be any the wiser. If you're patching or running it up against existing Loft White, get a tester pot, paint a decent A4 patch next to the old paint, and view it morning and evening before you commit. And whatever you choose, use the same finish throughout — a matt next to an eggshell will read as a bigger colour difference than the ΔE ever suggests.