There's no dead-ringer for Mylands Amber Grey No.156 in the Dulux range, but you've got two honest contenders.
The closest is Dulux Common Dormouse at ΔE 2.9, LRV 24.8. Right behind it is Dulux Urban Walk at ΔE 3, LRV 22.9. For context, a ΔE under 1 is imperceptible and under 2.5 is what I'd call a very close match — so both of these sit just outside that bracket. They're in the neighbourhood, not in the same seat. Stand them next to the real Amber Grey on a wall and you'll clock the difference; live with one on its own and you'd never know.
Between the two, I'd lean Common Dormouse — it's the tighter match on the numbers and the LRV (24.8) means it'll bounce light much the same way Amber Grey does. Urban Walk is fractionally deeper at LRV 22.9, so it reads a touch heavier in a north-facing room.
Now the honest bit: Mylands paint and Dulux paint don't behave the same in the tin. Mylands has that lovely depth of pigment and a soft chalky settle that's part of why people fall for Amber Grey in the first place. Match the colour in Dulux and you'll get close on hue, but you won't fully replicate the character. If it's a feature wall or a room where the finish really matters, it's worth asking yourself why you're switching — usually it's price or local stock.
My advice: buy sample pots of both Common Dormouse and Urban Walk, paint big A2 boards, and view them morning and evening against the original Mylands swatch. Two coats minimum — these greige-browns shift a lot between one coat and two. If you can stretch to it and you love the original, just buy the Mylands. A ΔE of around 3 is a compromise, and on a colour with this much warmth and subtlety, compromises tend to nag at you.