Will any flavour of Linux allow me to read and play the saved files on my Humax Fox T2 HD set top box?

No only using the CF to decrypt them by fooling the box into thinking it's a HDR FOX T2 will do that. Once decrypted you can play them on a PC with suitable media player software.

I don't think I framed my question very well. My set top box has a USB connected external hard drive. I just want to know if I connect the external drive to a Linux computer will it need to be a particular version of Linux or will any Linux do?

No problem understanding your OP. Your problem is nothing to do with Linux. Yes if you connect your external HDD to a PC that can read EXT3 volumes you will be able to see the transport stream files (.ts) that contain the video/audio content. If you try and view them on anything else you won't be able to do anything else with them. because the box decrypts all recorded content so you can only view it on the box that recorded it. The file system used to store the recording (in this case Linux ext3) has zero relevance. Without removing the encryption enforced during recording as described above the files will be useless.

I think you mean encrypts. Whilst they are encrypted you can only play them on the box that made the recording. The only practical way to decrypt the data is as Graham has already said to use the custom firmware and invoke HDR mode.

Thanks - yes encrypts of course.

Is this a Humax decision to encrypt the files or the broadcasters enforcing it?

I doubt that it is Humax who have unilaterally decided to add encryption; what would the advantage to them be?

A condition on a recorder box using the freeview HD epg is that the box allows broadcasters to dictate whether or not HD programmes are encrypted when recorded.
Read here for a bit of detail: http://en.wikipedia.org/wiki/Freevie...opy_protection

Humax have gone further and encrypted everything. An alternative would have been for the HD-Fox-T2 to not encrypt any standard definition programmes, and for HD programmes only to be encrypted if the broadcaster's metadata flags that it must be encrypted.