Good news ladies!
It is indeed a bad case of angry cervix.
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...
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.
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!
Thankyou so much for your kind words and support, wish you were on my other sodding thread, where most people are pretty much complaining about lack of symptoms. I'm just grateful the peanut is ok. Plus now we can sing the peanut vendor song to it every day.
Moo good luck with your testing, but remember, if you did implant yesterday, that's only 3 days, so HCG won't have had much chance to build up. Mine showed up as light pink line on IC 7 days post implantation.