There's no perfect Dulux twin for Green Smoke, but your two best bets are Dulux Mouse Tail (LRV 21.3, ΔE 4) and Dulux Midnight Garden (LRV 21, ΔE 4.7).
Let me be straight with you about those numbers. A ΔE under 1 is imperceptible, under 2.5 is very close. At ΔE 4, Mouse Tail is in the ballpark — you'll read it as the same kind of colour — but put the two side by side on a test board and a sharp eye will spot the difference. It's not a forensic match. So if you're touching up an existing wall already painted in Green Smoke, don't swap to Dulux and expect it to disappear into the old coat. It won't.
Green Smoke is that lovely smoky grey-green that goes properly moody in low light and lifts in the sun. Mouse Tail captures the muted greyed-green character well, and the LRVs are usefully similar — both sit around 21, so you'll get a comparable depth on the wall. Midnight Garden leans a touch more towards the green side of the family, which is why it sits slightly further out at ΔE 4.7.
The "but what about" question I always get here: why match to Dulux at all? Usually it's budget, or you want Dulux Trade's coverage and washability for a high-traffic spot. Both are fair reasons. If you're after the genuine F&B finish and depth, though, nothing beats the real thing — the pigment load and the way it shifts with the light is part of what you're paying for.
Practical advice: get sample pots of Mouse Tail and Midnight Garden, paint two coats on lining paper, and live with them for a couple of days. View them morning and evening, north and south light. With a ΔE this side of 4, your eye decides — not the spec sheet. Whichever reads closest to the Green Smoke in your room, that's your match.