I have a number of music CD disks, which take up a large amount of space. I hence want to burn all this music to a single larger disk so that these CD disks do not take up as much space in my car. Is it legal to burn music from all these CD disks to a single source, for my personal use?
Assuming that the music is protected by copyright, as almost all modern music is, that would be making a copy without permission, and would be an infringement of copyright. In the UK the US doctrine of "fair use" does not apply. The UK exception to copyright known as "fair dealing" is more limited, and I do not think that making such a copy would be covered by that exception.
However, copyright infringement (except on a large commercial scale) is a tort, not a crime. The police do not arrest a person for making unauthorized copies of CDs. The copyright owner would have to learn that the copy had been made, and file an infringement suit. This would require paying court fees and lawyer bills. The possible damages for such an infringement would be small. Will not impossible, such a suit seems a bit unlikely. If a person stated making multiple copies and handing them out to others so that sales of CDs might be harmed, legal action would be far more likely.
So the action would be technically illegal, but enforcement would be somewhat unlikely.