OK, might have fixed it, I'm not certain what I did though. I tried vol up + vol down + power and I got it to boot.

I'd not used my E4.5 for a while. Booted it and it looked fine, but I thought I'd run an update. I downloaded the installer snap to my Ubuntu desktop, and did a very normal installation. Rebooted, and it looked good.

Picked it up this morning and it won't boot. I get the "bq powered by ubuntu" boot screen but no further. Vol Up & Power gives me a boot menu (recovery, fast, normal) but vol down & power just reboots to the same point.

Have I bricked it, or is there a way out of this?