If you're after a Dulux stand-in for Paint & Paper Library Blue Blood, the colour you want is Dulux Moody Cobalt (LRV 15.9). It lands at ΔE 1.3 from the original — and anything under 2.5 is considered very close, so you'd be hard pushed to tell them apart on the wall.
Running neck and neck is Dulux Pebble Drift 1, also LRV 15.9 and also ΔE 1.3. The two are effectively interchangeable as matches on paper, so the deciding factor is finish and where you're buying. Moody Cobalt is the more obvious like-for-like by name and intent — go with that one as your first pick.
A word on why these are deep colours: at LRV 15.9 Blue Blood is a properly saturated, dramatic blue. That low light reflectance means it'll drink the light in a north-facing room, so it sings best somewhere with decent natural light or where you're *deliberately* going for cocooning drama — a dining room, a snug, a study.
Now the honest bit. A ΔE of 1.3 is a genuine match under standard light, but Paint & Paper Library and Dulux build their colours from different pigment recipes. In low evening light or under warm bulbs, a deep blue can shift subtly — one might read a touch more violet, the other a touch greener. Always buy a sample pot of the Dulux match and paint a big A2 patch, then live with it for a couple of days across morning, afternoon and lamplight before you commit.
If budget's the reason you're switching, that's fair — Dulux gets you the same colour for less. But if it's the *depth and finish* you fell for in the Paint & Paper Library original, their pigment density in a proper estate or eggshell finish is part of the appeal, and that doesn't fully transfer. Match the colour, yes — just go in eyes open on the feel.