Just to say what I've done in case it helps anyone else here. I tried and failed with several methods but came good in the end.
First off I tried the Chrome video downloader extension and managed to download one lesson of one class. but then it refused to download anything in full. I think it was happy with the short 6 minute intro but it gave up during the longer lessons. Next...
@Kwaaked's method unfortunately wouldn't work for me although I watched the video and followed her instructions faithfully. I think I probably needed to download the curl executable for Windows and I felt I'd spent enough time on it by then. I know this works well for many but I decided to move on. Next...
I tried two free video downloader apps but they wouldn't recognise the Bluprint videos as videos. So...
...following a suggestion on Pattern Review, I downloaded the Opera browser and its extension Flash Video Downloader - that took two minutes. It's simple and it works well. The first couple of classes took me a while as I worked out how to refresh the page for each lesson and check that I was downloading the right lesson. But I've done ten classes now and I'm pleased to have found a method that works for me. Each class of 7 or 8 lessons takes me about ten minutes. The lessons are already named - I just number them and create a folder for them. That takes two minutes.
So less than 15 minutes a class. Not as fast as Kwaaked but I probably wouldn't be anyway.
I have another 20 classes to go, some of which I may not bother with. I bought a 1T hard drive which I needed anyway and I'll load them onto that when it arrives. Maybe Bluprint will come up with something but then maybe they won't - I'd give it 50-50.