I am thinking of upgrading from Lightroom 4 to Lightroom 5. I want to know if it is possible to either buy a backup disc, or to generate one as part of the download process

you can burn you own disc with the installation file(s) (for your own use), but adobe no longer supplies discs

Downloads available:

• Suites and Programs:  CC 2014 | CC | CS6 | CS5.5 | CS5 | CS4 | CS3
• Acrobat:  XI, X | 9,8 | 9 standard
• Premiere Elements:  12 | 11, 10 | 9, 8, 7
• Photoshop Elements:  12 | 11, 10 | 9,8,7
• Lightroom:  5.6| 5 | 4 | 3
• Captivate:  8 | 7 | 6 | 5
• Contribute:  CS5 | CS4, CS3

Download and installation help for Adobe links

Download and installation help for Prodesigntools links are listed on most linked pages.  They are critical; especially steps 1, 2 and 3.  If you click a link that does not have those steps listed, open a second window using the Lightroom 3 link to see those 'Important Instructions'.