"Does the hallway have a plug socket or one in a room your could an extension cord from without tripping? I'd recommend a slim convection heater with timer and thermostat."
Yes, there's a plug in a nearby room. I already have a convection heater and a timer plug so I can do this. I don't have a thermostat for it, but if I timed it to come on for half an hour at a time before I get up or something it wouldn't overheat.
"Ditto the bathroom - before your shower you could warm the bathroom up with the convection (use an extension cord if necessary) but just remove it before you shower to avoid the heater getting moisture in it. Alternatively a fan heater?"
There is no reason to do this as I already have a heater in the bathroom that I turn on before and during my shower. The problem I have is that, like all my heaters, I cannot time it so I have to get up early to put it on then come downstairs.
Today, the whole flat was quite warm as I'd been at home all day with the heating on in both main rooms. Before my shower, I put my bathroom heater on too, but was still cold when I stepped into my walkin shower and I think it's coming from the fan. The bathroom fan comes on automatically when I switch the light on so the only way to avoid it would be to shower in the dark or get myself a separate light.
I then went out for three hours and came back to a cold flat. Hard to believe it's gone cold so quickly as it was really warm when I left.