Any idea why my Photinia is dying?

Is it in a pot or in the ground, and how long have you had the plant?

It's in the ground. Was in the garden when we moved in 2 years ago and was quite well established. It's spread is about 6ft by 6ft. Had a heavy prune in the autumn but there was fresh growth in the spring.

There may be trouble at the root, given there's nothing obvious showing on the upper branches and foliage, so its worth checking the woody stems right the way down to the base to see if there are any cracks, soft spots, weeping areas, that sort of thing, especially near the base.

You say you pruned it heavily last autumn - depending when you did it, that might have caused a problem. I'd leave it alone for now, but go out in midwinter, when its dormant, and cut it back by at least half. In spring, give it a good feed (assuming its still alive) and see how it goes.

Thanks for the advice.