Peugeot 206 1.4 hdi 2006 manual: intermittent doesn't turn over, lights on dash normal

You say battery is fine , what voltage is it showing ?

Hi, and thanks for your help.
It's reading 12.67V.

Battery reading is fine with that reading . All I can suggest is it could be a faulty "lazy " starter or wiring at starter . Could also check all earths , especially from engine to body . Other possibility is ignition switch , could try jiggling the key when it acts up . Intermittent faults can be a devil to find at times . There are also a few fuses that cover the ignition switch in different locations according to this ( if it applies to your car ) Could check their security by pushing by hand ,
https://fusesdiagram.com/peugeot/fuses-and-relay-peugeot-206.html

Thanks.
I already wiggled every fuse I could see, but there are some more in your link that I hadn't noticed: maxi-fuse 1-8.
I hadn't tried wiggling or whacking the key and ignition.
I suspect it's a fault in the starter motor, or the wiring to that. I'll have to find where that is.
Nice one!