BBC iPlayer Downloads app - downloads unplayable in iTunes or QuickTime etc?

I'm not sure if this is the correct forum, but as iTunes is involved I'll take my chance.

I have a late 2009 quad-core i7 iMac with 1TB HD and 16GB RAM running under MacOSX.10.01.4 Build 14E46 and I am using iTunes v12.2.1.16 and BBC iPlayer Downloads 1.14.0

I can download programmes just fine. Well, let me rephrase that - programmes doanload in two files, for example:

bUnknown-5525b4eb-c7da-4ae8-89d1-5e3f039b64d5_b0658f11_1438719656858.xml 120KB XML text

bUnknown-1004f6f6-2131-4e2a-a204-3703ee3387dd_b06496b6_1437457436228.mp4 1.02GB MPEG-4 movie

Those two may not be related as I have three of each in my ~/Movies/BBC iPlayer Downloads folder and, as you can see, the filenames are meaningless to a mere mortal such as me.

If I open the *.xml file the rather scary X-Code opens and I quit before I do any damage!

If I open the mp4 file, QuickTime Player v10.4 (833.6) opens and "converts" the file into a playable format which consists of one hour of a perfectly white screen with no sound.

If iItry and import the mp4 into iTunes, I click the Import option and ... nothing happens. The file isn't imported and nor does it play.

I've looked around the circuitous and somewhat user hostile BBC iPlayer help pages and found nothing that might explain what is happpening.

How can I download programmes ina format which a) has a proper file name so that i can identify the programmes and b) actually play them on my iMac?

Thanks in advance.