I should have posted this ages ago. There is a well known problem which may affect Nexus 4 devices where it powers off and won’t power on again. When you plug it into the USB charger you get a solid red light and it never recovers.
If you search for the problem the main advice is to return the phone for a factory fix, however there’s an easier trick that’s worked for me; using a wireless charger.
Every time I’ve had this problem (on a few different Nexus 4 phones) I’ve been able to bring the phone back by sitting it on my Nexus wireless charger for a few minutes, then pressing the power button and it springs to life.
After that, you can charge and use the phone as normal. I am writing this now because I was reminded after using this trick to fix a friend’s phone tonight (he’d been googling the problem for a while with no luck).
Maybe someone still has one in their bottom drawer and can make use of it again by using this trick!