Empire Grey No.171 is one of Mylands' lovely warm-leaning greys with a soft brown, taupe undertone, but Mylands sits at the premium end and you don't always need it. If you're after the look without the spend, Dulux Bleached Lichen 1 is your best bet — it lands at ΔE 2.3 from the original, which is very close indeed. To the eye, in most lights, you'd struggle to tell them apart on a finished wall. And Dulux trade emulsion will cost you a good chunk less per tin.
If low-VOC matters to you — nursery, bedroom, someone in the house sensitive to smell — go for COAT Cold Brew (LRV 32.1) instead. It's a touch further off at ΔE 3.4, so a small but noticeable shift, but COAT's a genuinely good water-based paint with a clean finish and zero faff on application. Worth the slight compromise if eco-credentials are the priority.
I'd steer you away from Crown French Grey here. It's a perfectly nice colour in its own right (LRV 38.5), but at ΔE 4.5 from Empire Grey it's a clearly different shade — more obviously cool and lighter on the wall. Specify it if you actually like *it*, but don't buy it expecting an Empire Grey dupe, because it isn't one.
The usual caveat applies, mate: these matches are measured against the original, but finish and brand formulation change how a colour reads. Mylands has a particular depth and chalkiness in its Marble Matt that a standard Dulux vinyl matt won't fully replicate. If that richness is what drew you to Empire Grey in the first place, the difference will be in the *texture* as much as the hue.
Practical advice: order a sample pot of Bleached Lichen 1, brush out two coats on lining paper, and tape it up next to a Mylands sample card on the actual wall. Look at it morning and evening before you commit a full room.