Honest answer, mate: Dulux doesn't have a proper twin for Little Greene Hicks' Blue. The nearest in our database is Dulux Azure Fusion 1 (LRV 5.4) at ΔE 8.7 from the original, with Dulux DH Oxford Blue (LRV 3.8) further off at ΔE 11.7. 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 the moment you put them side by side.
What's going on is that Hicks' Blue is a deep, muted slate blue — softened with grey, more smoke than jewel — and that's exactly the character the Dulux blues miss. Azure Fusion 1 is the closer of the two, but it reads darker and more saturated, without that grey-tempered softness. Oxford Blue (from the Dulux Heritage range) is a handsome saturated dark navy in its own right, but at ΔE 11.7 it's a different colour altogether — flatter, cooler and deeper than the Little Greene.
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 Azure Fusion 1 — it's the nearest, just don't expect a dupe. If you want something deeper and moodier and you're not chasing Hicks' Blue exactly, Oxford Blue stands on its own merits.
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.