Hi there.
Sorry you are having a stressful time.
Firstly, with regards to your currently assessed risk; the NHS often won't reduce a risk in my (limited) experience. This doesn't change the fact that the second consultant getting lower measurements is a good sign.
We had an NHS scan with a measurement of 2.2mm or so, but high risk blood results (1:35) and went to the FMC clinic in London just over a week later for another scan. They measured 3.6mm, so things changed quite fast for us too. We had a re-assessed risk of 1:2 from the FMC, but thankfully the tests all came back clear.
Maybe try to find out specifically what your blood test results were. They will have measured two hormones and will give you measurements for how many times the average measurement (MoM) you are (for your stage of pregnancy). This will help you better understand the risks.
If you are keen to do something then as AndIFeedEmGunpowder said, you could consider the Harmony test. Will cost £400 from FMC and is 99.9% accurate. But the results take time, so if you are going for CVS/Amnio anyway then I'm not sure it will get you any more info any sooner.
Alternatively FMC could do CVS/Amnio (as PenguinsDontEatPancakes ti sounds like it is CVS they can't do currently) - this would cost you £400. Initial results (including DS) take 2-3 working days.
Or they could do another scan which would cost £180. They have great consultants and equipment. We phoned for one of these on a Weds and had the appointment 2 days later on the Friday (got initial results on Tuesday). If you're near London then it might be worth it just to get more info and maybe reassure you.
Lastly - remember that with the worse measurements they are giving you an assessment that everything is 80% ok. With the second measurements things would be even higher. Things are quite likely ok. Fingers crossed.
Let us know how you get on. I hope it all goes well.