Good news ladies!
Everything's fine.
I couldn't see anything on the screen because the sonographer had all the sympathy and humour of an east german ex-shotputter, plus she had the machine facing the wrong way for me. Inserted the probe like she was stuffing a turkey...
But DH got a really good look. And...
We have a peanut. 
In the right place

With no bleeding

...And a heartbeat!

Leaflet at hospital says I have an 85-97% chance of this all working out fine.
I am so relieved!!!
Plus it turns out I haven't had the right phone number for the EPU, which is why I couldn't get through. I've alerted them to it though now.
They said they thought the bleeding was implantation, but that doesn't sound right to me. I think the earlier possible diagnosis of angry cervix is more plausible, considering the spotting variations over the past week.
SiL dropped us home and stayed for lunch, where she pointed out that my spotting started when my MiL came to stay... if it's stopped tomorrow, I think we know what the cause was! Frightened now though, as she'll be back at the beginning of March... on and off for 5 months. REALLY hoping it's not her causing it!
Thanks for all your best wishes, I'm sure they helped me through. X