China Clay is one of Little Greene's loveliest off-whites — a soft, warm, milky cream that sits beautifully on walls without going sterile. But Little Greene isn't cheap, so I get why you're after an alternative.
The best match by a country mile is Dulux Desert Vista (LRV 85.6), which comes in at ΔE 0.9 from the original. Anything under 1 is imperceptible to the naked eye — you genuinely would not be able to tell them apart on the wall. Dulux is widely stocked, the trade prices are friendly, and you'll get Diamond Matt or Easycare for kitchens and hallways. For a near-identical colour at a fraction of the cost, that's the one I'd reach for.
If Dulux isn't your bag, Crown Cream White (LRV 85.8) lands at ΔE 2 — still very close, the difference being a whisker more in the undertone. Crown's Easyclean Matt is a genuinely good wipeable finish for family spaces.
And if you want something low-VOC and a bit more eco-minded, COAT Cat's Cradle (LRV 85.2) is ΔE 2.1 — water-based, low odour, and they sell sample pots so you can test before committing.
The usual caveat: these are excellent colour matches, but they aren't matched on finish and depth. Little Greene's pigment load and the way their paint sits — particularly in their Intelligent and Absolute Matt finishes — is part of what you're paying for. On a feature wall in good light, a sharp eye might notice China Clay has slightly more presence. On a hallway or bedroom, nobody's clocking the difference.
My advice: order a sample of Desert Vista, paint two coats on a bit of lining paper, and prop it against a China Clay card. View it morning and evening before you buy the lot. At ΔE 0.9 I'd put money on you not seeing a difference — and you'll have saved a tidy sum.