If you want a Dulux stand-in for Little Greene Bone China Blue, go for Dulux Steel Parade. It lands at ΔE 2.6 from the original, which is genuinely close — close enough that most people wouldn't clock the difference once it's up on a wall. Steel Parade carries an LRV of 47.3, so it sits comfortably in that mid-tone bracket: enough light bouncing back to keep a room feeling open, but with proper presence rather than washing out.
The runner-up is Dulux River Valley at ΔE 3.4, with an LRV of 43.1. That's a slightly bigger gap — you'd notice it side by side — and it reads a touch deeper and moodier. Worth a sample pot if you're after a cosier, more grounded version of the same blue, but if you're chasing a true match, Steel Parade is the one.
Now, the honest bit. Bone China Blue is a soft, slightly chalky powder blue, and Little Greene's pigment depth is part of why people love it. A ΔE of 2.6 is a strong match on paper, but the two paints won't behave identically in changing light — Little Greene's colours tend to shift more gracefully through the day thanks to their pigment load. In a north-facing room especially, Steel Parade may feel a little flatter and cooler. South-facing or well-lit spaces close the gap considerably.
So my advice: order sample pots of both Steel Parade and River Valley, paint them onto a couple of A4 boards (not straight onto the wall — you want to move them around), and check them morning and evening against your existing trim and floor. If the match has to be spot-on and the budget allows, the real Bone China Blue is the safer call. But if Dulux is your spec, Steel Parade does the job properly.