My neighbour pointed out that one of my potted conifers was not thriving.
To be fair this plant has always been a "problem child" - I bought it at a discount because it was in poor condition - but I decided it was worth checking the pot to see if there were any obvious causes.
It had quite a few weeds around it but no other obvious problems so I took it out to look at the roots:
Not root-bound but a bit water logged. An examination of the pot revealed that it only had 4 small drainage holes and these were completely clogged up:
I made the holes larger, added a few more and lined the base the pot with plenty of broken-up polystyrene, then re-potted the tree:
Hopefully the tree will now improve, I'll post an update in a couple of months to let you know how it gets on.