I'm losing my blueberries!

Bought 4 assorted from Ken Muir early last year and they've been very healthy. Even got a bit of fruit on a couple this year.
Then I noticed one of the two "Herberts" was going brown and it got worse even with tlc.
Eventually I dug it up and moved it to a pot of ericaceous compost and gave it a good water but it was pretty dead and hasn't survived.. Now the other Herbert is curling up it's toes so I think I'll whip it out smartish.
The Earliblue and Blueboy seem unaffected but they're a bit away. It's not water or soil. Branches are spreading black/brown from the tips and leaves are curling and going soft and brown.
Is this a blueberry disease or could the damson and plum near them that haven't been well be infecting them?

Hi.

You said "Eventually I dug it up and moved it to a pot of ericaceous compost and gave it a good watering...".

Where did you have it planted first - in ordinary soil? Was it fed with food suitable for acid loving plants? Has it been kept well watered always and only with rain water?

All of these things are important to blueberry plants.

I've looked in Ken Muir's book borrowed from a mate and I think it's Blueberry stem blight.
As with other blights the spores travel in rain and wind and will latch on to any wound in a healthy plant. The description of symptoms fits perfectly.
I have a blight of sorts on the plum and blight on the toms and potatoes so I'll blame it on this dreadful year and get rid of the infected plants asap!
(By the way.....the plants are in nice acid soil and get watered with rain water.....possibly too much this year!)

They ARE in acid soil at the edge of a conifer tree. They have a thick pine needle mulch and I do everything by the book!
My soil is acid all over the garden actually which is proved by the profuse growth of the rhododendrums and azaleas.
This is definitely a blight, not a maintenance prob.
Threw away another few pounds of toms today..........

I have experienced exactly the same, I lost one plant and cut back the other two plants which did resprout and recover.  I couldn't find a cause at the time but it sounds like you have had more luck tracking down the problem than I did at the time.