Yep, I'm definitely flashing the sailfish .simg.
After reflashing the stock rom and trying again, the phone no longer boots into UT but hangs at the 'Powered by Android' screen. When It's connected to a computer it appears as a media device with the name 'Failed to boot'.
I haven't had any problems flashing UT or stock.
I might have done some strange things with fastboot in my frustration over the last few days, could anything there be the cause? I assumed flashing stock would restore everything to factory condition but I might be wrong there.