First off, congratulations!
I've had 12 week nuchal scans at FMC with all 3 of my pregnancies, and they're fantastic. The quality of the scan and machines is excellent (I work in the field) and by the end of the scan you'll have a detailed risk assessment of the likelihood of abnormality. My NHS scan was perfectly adequate, but I was simply given a "high"/"low" risk which wasn't detailed enough for me.
With DC2, I was 40 and the nasal bone wasn't visible on the 12 week scan, giving me a risk of 1/300. I know a lot of people would be happy with that, but the absent bone really worried me and I had a CVS at FMC a few days later. In total it cost about £500 for the nuchal scan and CVS, but the Prof himself always does them (unless on leave etc) and he has an extremely low miscarriage rate.
I'm now almost term with DC3 at the age of 41. In view of what happened last time, I booked myself in for both a nuchal and a CVS straight off as I was convinced the risks of abnormality could only be higher than before. As it turned out, my risk was waaaaaay better than expected for age, so on the day we decided against proceeding to CVS. I hope it was the right decision.
A CVS is not without risk, and not to be taken lightly, but at FMC you are in the hands of a world leader. I would do as others have suggested, have your nuchal and take it from there. As regards then having a CVS, It's whether you have the funds to go private. At FMC the Prof does all the procedures on a Wednesday, and you get the results that Friday. I can't comment on George's, but NHS elsewhere usually takes longer.
Another point to consider is that I believe FMC are offering the Harmony test now too, where they look for fetal DNA in a blood sample from you. It is meant to be extremely accurate and may reassure you without the need for a CVS at all.
I think it all depends what level of risk you are happy with, and what degree of certainty you need; also whether it would alter your actions as regards your pregnancy.
Apologies for the essay, but having been through it I fully sympathise. Am happy to answer any other questions..
HTH