If you want Chiltern White in standard Dulux, reach for Cotton Bloom. It comes in at ΔE 0 from Dulux Heritage Chiltern White, which means there's no perceptible difference between the two — they're the same colour for all practical purposes. Cotton Bloom has an LRV of 71.7, so it's a soft, light off-white that'll bounce plenty of light around a room without tipping into stark brilliant-white territory.
If Cotton Bloom isn't to hand or your stockist hasn't got it mixed, Ashen White is the next best thing at ΔE 1 — still imperceptibly close (anything under 2.5 reads as a very tight match), with an LRV of 71.6 that's near enough identical in lightness. You'd struggle to tell the two apart on a wall.
So why bother with the Heritage line at all if standard Dulux nails the colour? Mostly it comes down to finish and feel. Dulux Heritage paints have a slightly different formulation — a flatter, chalkier matt and a more pigment-rich body — so if you're after that softer, more characterful look on a feature wall, the Heritage tin earns its premium. But if you're painting a hallway, a rental, or a big trade job where budget matters, matching to Cotton Bloom in standard Dulux Diamond Matt or Trade gets you the same colour at a friendlier price.
One thing to watch: light off-whites like this shift with the light they're sitting in. In a north-facing room Chiltern White (and its matches) can read a touch cooler and greyer than you'd expect from the chip. Always get a sample pot up on the wall — paint a decent-sized patch, view it morning and evening — before you commit a whole room. Don't judge it off the lid.
For the record, both matches are verified against the original, so you can buy with confidence.