If you want to get near Farrow & Ball Off-Black without paying F&B prices, Dulux Charcoal Drift is your best bet. It lands at ΔE 2.5 from the original (LRV 7.6) — that's just inside the "very close" threshold, so most eyes won't clock the difference on a wall.
Runner-up is Dulux Basically Black at ΔE 2.7 (LRV 7.3). Still a cracking match, just a whisker further off — it reads a touch flatter and a fraction darker, where Charcoal Drift holds onto that subtle greenish-grey warmth that makes Off-Black so good. Off-Black isn't a true black, mate — it's a deep, soft near-black with a green undertone, which is exactly why people love it for woodwork and panelling. Charcoal Drift respects that better.
But here's the honest bit: a ΔE of 2.5 is close, not identical. The thing that actually separates Off-Black from a Dulux respray isn't the pigment — it's the finish. Farrow & Ball's Estate Eggshell and Dead Flat have a chalky, light-eating depth that Dulux's standard sheens don't quite replicate. At this kind of LRV (high single figures), the difference shows most under raking light on a low-sheen surface. So if you're matching Off-Black on a feature wall, Dulux gets you there. If you're matching it on intricate panelling where the finish is the whole point, the gap widens.
My advice: order a Dulux Charcoal Drift tester and paint a decent-sized board — at least A3 — then stand it next to your existing Off-Black under both daylight and your evening lamps. Dark colours shift more than people expect between light sources. If you're doing trim or doors, spec Dulux in a satinwood or eggshell to get closest to the F&B feel.
One last thing: don't skimp on prep with near-blacks. Any patchiness in the substrate shows through dark colours mercilessly, so prime properly and use Zinsser Cover Stain if you're going over anything dodgy.