If you want Milk White on a Dulux budget, Elderflower Tea is your answer. It comes in at ΔE 0.2 from the original — that's well under the threshold of 1 where the human eye can spot any difference at all. To all intents and purposes they're the same colour.
Worth knowing: Salisbury Stones 5 lands at exactly the same place — LRV 72.4, ΔE 0.2. The two Dulux colours are effectively the same shade under different names (one sits in the standard collection, the other in a tinter range), so pick whichever your stockist mixes most readily. Both share Milk White's LRV of 72.4, meaning they bounce the same amount of light around a room — you won't get a surprise when it goes up on the wall.
Here's the honest bit, though. Edward Bulmer's whole thing is natural, plant- and mineral-based paint with no acrylic binders, and that gives Milk White a particular soft, chalky depth that's hard to fully replicate in a conventional emulsion. A spectrophotometer reads the colour, not the *feel* of the finish. So while Elderflower Tea will match the hue beautifully, the surface quality will be a touch flatter and more plasticky by comparison. If it's the eco credentials and the chalky look you're after rather than just the colour, that's a reason to stay with Bulmer.
But if you simply love the shade and want it in a hard-wearing, wipeable kitchen or hallway finish at a lower price, Elderflower Tea in Dulux Diamond Matt is a cracking substitute.
As always with a colour match: buy a sample pot, paint two coats on a bit of lining paper, and move it round the room over a day. Milk White is a warm off-white, and warm off-whites can read quite differently in a north-facing room versus a sunny south-facing one. Trust the wall, not the chip.