When I have several recorded programmes on a disc and erase some after watching it no longer combines the erased portions into one complete erased sections, sio I get lots of individual portions.

This probably varies with different types of recorders but the older models we have will only combine erased segments that are next to each other on the disc menu. In other words, if we had 3, 90 minute movies recorded and 30 minutes of unused space at the end--then erased the 2nd movie, we would end up with a 90 min segment and the original 30 minute segment at the end. If instead, we erased the last movie, we would have a now 120 minute space at the end. I am certainly not an expert on this issue but the above is how our machines work.

It also depends on the type of disc you are using. For maximum editing capabilities through a DVD recorder, use DVD+RW.