Back from my holidays so I had a go at this Fairport CD which I burned 20 or more years ago and which showed periods of distortion when I played it recently with the CD player attached to the amplifier in my living room.

I put it in the optical disc reader in my desktop computer and played it on that. There were quite a few gaps and jumps in the music.

The disc looked pristine - it has been kept in an individual plastic case. I washed it with washing-up detergent and water. The result was no distortion on CD player. The computer still appeared to detect faults - the seconds counter kept pausing - but it managed to keep playing with no audible (to me) gaps or artifacts.

So thanks for the suggestion, SRS. I shall do that if I find more distorted ones.

I conclude that washing the CD improved it enough for the CDDA error-correction in the players to work but that the disc is still faulty. (It might of course have been equally faulty when I burned it.) I wondered if there was a way of measuring the degree of faultiness? And if washing it hadn't improved it could I recover the music to some extent? I found this:
How to rescue audio CD

I copied track 1 of the CD to a wav file using cdda2wav and checksummed the wav file. I did that twice more and compared the checksums. All three wav files sound OK to me, but the checksums were all different.

cdparanoia (according to that thread) does this several times to arrive at a 'best' version. I did the same experiment with cdparanoia instead of cdda2wav and this time the checksums matched. So cdparanoia seems like a good tool to attempt to recover a failing CD.

cdda2wav and cdparanoia are ancient Linux tools. Windows and Mac versions may be available:
cdparanoia - Hydrogen Audio knowledgebase
Windows 10 or 11 users could of course install WSL and run the Linux version of cdparanoia.