If you love Sanderson Night Fishing but not the price tag, the one to go for is Dulux Amethyst Falls 1. It lands at ΔE 1.9 from the original — anything under 2.5 is very close, and at 1.9 you'd be hard pushed to spot the difference once it's dry on the wall and out of the tin. It also sits at LRV 5.8, so it's holding onto that deep, moody, near-black-with-a-purple-undertone character that makes Night Fishing what it is.
For context, the other near-matches don't really hold up as dupes. Crown Leatherbound comes in at ΔE 8.3 and COAT 2AM at ΔE 5.7 — both drift noticeably off the original, leaning into different undertones. They're handsome colours in their own right, but if it's *Night Fishing specifically* you're after, neither will scratch the itch. Amethyst Falls 1 is the only one of the three that's genuinely a match rather than just "in the same family".
Now, the honest bit: the colour is the easy part — the finish is where Sanderson earns its money. Dulux's trade ranges (Diamond Matt for walls, or Heritage if you want a richer, flatter chalky look) will get you a lovely result, but a budget contract emulsion in a deep shade like this can look patchy and flash under raking light. Deep, near-black colours are unforgiving — they show every roller mark and every thin spot.
So my advice: don't cheap out on the application even if you're saving on the tin. Use a deep-base tinted product, expect two solid coats minimum (possibly three on a deep shade), and prime over anything dodgy or stained first with a Zinsser primer so the base doesn't drink the colour unevenly.
Get Amethyst Falls 1 in a proper Dulux matt, do it properly, and nobody will know it isn't the Sanderson. Sorted.