If you want to put Lead V into a Dulux can, Steel Symphony 5 is your best bet — it lands at ΔE 1.8 from the original, with an LRV of 62. That's well inside the "very close" range (anything under 2.5), meaning the difference is genuinely hard to spot in normal room light.
Right behind it is Pale Slate at ΔE 2, LRV 59.8. Slightly less reflective, a touch deeper, but still a cracking match. Honestly, between these two you'd be splitting hairs — both read as that soft, cool grey Lead V is known for.
Why go Dulux at all? Usually it's budget, availability, or you're matching to a Dulux scheme already on the go elsewhere in the house. Paint & Paper Library is a lovely paint with real depth of pigment, so just be aware you're trading some of that nuance for convenience. Lead V has a quiet, almost architectural quality, and the Dulux matches get you 95% of the way there.
The "but what about the finish?" question matters here. ΔE only measures colour, not sheen. PPL's Architects Matt and Pure Flat Emulsion sit differently to Dulux's Diamond Matt or Heritage range — a higher-sheen finish will throw the colour cooler and lighter regardless of the match figure. So pick your Dulux sheen to mirror whatever you'd have used in the PPL.
Practical advice: order a sample pot of Steel Symphony 5 and brush it out on lining paper alongside a Lead V sample if you can get one. View it on both your brightest and dullest walls across a full day. Greys like this shift more with light than almost any other colour family, so the room will tell you more than the ΔE number ever can. If Steel Symphony 5 reads a hair too light for the space, drop to Pale Slate and you're sorted.