There's no perfect Dulux twin for Sanderson Eucalyptus, but the nearest you'll get is Dulux Sea Urchin 2 (LRV 26.2) at ΔE 3.7 from the original. That's a noticeable difference rather than an imperceptible one — anything under 2.5 reads as very close, under 1 as effectively identical, and 3.7 sits beyond both. You'll see it in a side-by-side, though on a wall on its own most people wouldn't clock it.
The runner-up is Dulux Soft Fauna 2 (LRV 23) at ΔE 4.2. It's a shade darker and drifts a little further from the source, so I'd only go for it if you specifically want a slightly deeper, more grounded green than Sea Urchin gives you.
Here's the honest bit, mate: with a ΔE this high, you're not really matching Eucalyptus — you're finding the closest neighbour in the Dulux fan. If the exact colour genuinely matters (say you're patching into existing Sanderson work), don't switch brands. Just buy the Sanderson and be done with it.
If the switch is about getting a trade-friendly, easily-stocked emulsion in a similar soft sage register, then Sea Urchin 2 is your pick. It holds that dusty, slightly grey-green character that makes Eucalyptus so easy to live with, and it'll behave nicely in a north-facing room without going cold and sad.
The but-what-about: green-greys are brutal for shifting with the light. Eucalyptus and its Dulux cousins can swing from soft sage in the morning to flat grey under cloud. So whichever you land on, paint a decent-sized sample patch — A2 minimum — and live with it over a full day before you buy the tins.
Match off a screen and you'll be disappointed. Always sample.