Tigsy - there's a place called Apeekaboo in Erith/Belvedere that both Lewisham hospital officially and the receptionist I spoke to at QE in Woolwich unofficially recommend. It's £80 for a viability scan and I've heard good things about them.
I totally get the tears thing, etc., and although I've decided not to have one this time, I was exactly that way last time after mc'ing at 11 weeks with my first, and it was worth every penny (and we paid twice that much because I didn't know about Apeekaboo and so a consultant at QE did it for us privately). It ended up being at 8 weeks 4 days and by that point we could see both hemispheres of the brain and a big flashing heart. It was my best scan - so wonderful! Although I agree with Wilhelmina that the 3/4D scans are a bit weird!
I would say it's worth waiting till you are sure you are at least 7 weeks as you can see so much more then. The problem with any earlier of course is that it could be inconclusive and then you'll just have more worry (I have a feeling you said upthread that you're a doctor so I'm sure you know all that!)
Also, although seeing a heartbeat at 8 weeks is no guarantee, it does mean something like a 95% chance of success, which is fairly reassuring.
LittleMiss I'm just about 6 weeks now and I'm starting to feel really tired, although the bloating and wind have completely disappeared. I'm not sure if it's because I have a grotty cold, but I'd really just like to go to bed for a couple of days right now.
In both of my previous pregnancies I've only have very mild symptoms which wouldn't necessarily have made me think I was pregnant if I didn't know, but like someone else said, unless symptoms are strong you do tend to ascribe everything to the fact that you're pg. I often feel like I want to go to be for a couple of days 