The nearest Dulux colour to Mylands Brompton Road No.205 is Dulux Forest Shade (LRV 11.3), sitting at ΔE 3.2 from the original. That's close but not perfect — anything under 2.5 is what I'd call very close, and under 1 is imperceptible, so at 3.2 you'll spot a subtle shift if you put the two side by side. In an isolated room, away from the Mylands chip, most people wouldn't clock it.
The runner-up is Dulux Holiday Bough (LRV 12.7) at ΔE 4.7. That's a noticeable step further off — enough that I'd only reach for it if Forest Shade isn't available in the finish you need.
Here's the honest truth, mate: Brompton Road is a deep, characterful Mylands green, and Mylands paints carry a depth of pigment and a subtlety of undertone that trade emulsions don't always replicate cleanly. A ΔE of 3.2 means Forest Shade is the *closest* Dulux gets, not that it's a like-for-like swap. The undertone and the way it shifts in changing light won't be identical.
Why go Dulux at all? Usually cost, availability, or matching an existing spec. If that's you, Forest Shade is your pick — order it in Dulux Heritage quality if the finish allows, as the Heritage line holds deep colours better than standard trade emulsion.
But if you genuinely love Brompton Road, my advice is don't compromise. Buy the Mylands. Their dark greens are some of the best in the business and you'll notice the difference on the wall, especially in a north-facing room where depth really earns its keep.
Whatever you choose, get sample pots of both Forest Shade and Holiday Bough, paint two coats on a bit of lining paper, and view them at different times of day next to the original chip. ΔE figures are a brilliant shortlist tool — but your own eye in your own light is the final word.