Honest answer, mate: Dulux doesn't have a proper twin for Little Greene Hicks' Blue. The two closest in our database are Dulux DH Oxford Blue (LRV 3.8, ΔE 9 from the original) and Dulux Azure Fusion 1 (LRV 5.4, ΔE 8.7). Anything with a ΔE under about 2.5 is what I'd call a genuine match — these are well north of that, so you'll see the difference if you put them side by side.
What's going on is that Hicks' Blue is a deep, slightly purpled inky blue with real depth and a bit of warmth to it — that's the Little Greene character. Oxford Blue (from the Dulux Heritage range) is the better starting point because it's a similar saturated dark navy, but it reads a touch flatter and cooler. Azure Fusion 1 is marginally lighter and a little brighter — closer on the colour meter but it loses some of that brooding depth that makes Hicks' Blue special.
Here's the thing though: at this depth of blue, paint quality and pigment richness matter as much as the hex value. Little Greene's Intelligent Matt and Absolute Matt have a pigment density and chalky finish that's genuinely hard to replicate in a standard Dulux trade emulsion. You're not just buying a colour, you're buying the way it absorbs and sits on the wall.
So my advice: if the spec says Dulux for warranty or contract reasons, go DH Oxford Blue — it's the truer character match despite the slightly higher ΔE. If you want a hair more lift in a darker room, Azure Fusion 1.
But if there's any flexibility at all, just buy the Hicks' Blue. Brush out an A4 sample of all three on the actual wall, view it morning and evening, and you'll see why I'd spend the extra. Dark blues shift hard with light — test, don't trust the chip.