If you're after a Dulux stand-in for Sanderson Scotch Grey, go with Dulux Shingle Steps. It comes in at a measured ΔE of 1.2 from the original — that's well under the 2.5 threshold where a difference becomes genuinely hard to spot side by side, mate. On a wall, in real light, you'd struggle to tell them apart.
The close second is Dulux Goose Down at ΔE 1.3. Honestly there's barely a cigarette paper between the two, so don't agonise. Both sit at almost identical lightness — Shingle Steps at LRV 58.9 and Goose Down at LRV 59.3 — which is exactly why they read the same as Scotch Grey. That's a soft, mid-pale grey with enough warmth to stay friendly rather than clinical.
The usual "but what about" here: why match in the first place? Two reasons people do it. Either you've got a Sanderson colour you love but want it in a more widely-stocked Dulux base for cost or availability, or you're mixing into a Dulux trade system across a job and want everything from one tin range. Both are sensible. Just don't expect a 100% identical experience — Sanderson and Dulux use different bases and resins, so sheen and depth can shift subtly even when the colour reads the same.
My practical advice: always brush out a tester before you commit the whole room. A ΔE of 1.2 is a lab figure measured under controlled light. Your north-facing landing at 4pm in November is not a lab. Paint two A2 patches — one Shingle Steps, one Goose Down — on lining paper, move them round the room over a day, and pick whichever holds up best in your actual light. For greys in this lightness band, north light can pull out a cool blue cast and warm afternoon sun can flatten it, so seeing it across the day matters more than the decimal point.
Get your patches up, live with them a couple of days, then crack on.