Hello Harry,
Don't know if this will help your situation, but I have a similar situation / path.
Over 40 family years of 504 Cabriolet (Ti engine) we had exactly the same-sounding issue. Car would start fine from cold, but when warm, turning the key would not start the engine.
We employed the tactic of opening the bonnet and pulling the electrical cable from the injector that is found at the end of the inlet manifold
this is nearest the windscreen) and whose job is to inject petrol (for a period of time) directly into the intake manifold, and thereby enrichen the air/fuel mixture.
This action would let the engine start, and all we had to do was reconnect the cable when we wanted to start the car from cold another time.
Years have gone by, and the problem got worse and worse.
Discovery:
I THINK that the issue was that the injection system was becoming 'rich' and that the additional raw petrol being injected at starter engagement made the mixture too rich.
In my case,I have discovered a number of problems, that cause the injection system to put too much fuel into the engine.
The number one issue was a leak in the two (larger) membranes that are in the section of the pump which is manipulated by the flow of air from the Altimeter to the Inlet Manifold (I don't have a picture to hand as I write this, but it the top part of the pump that has a DOME on top of it)
You can do a non empirical check of the membrane integrity by doing this disgusting thing !!! Disconnect the pipes from the Altimeter and the manifold. suck / blow in them and there should be minimal air travel (if that makes sense) if there is a leak, air will flow through the system , rather than move the components... (phew, this is sounding long winded)
I found that my membranes were fractured, and a change sorted it ALL out, massive difference.
I have pictures of all this stuff, LMK if they would help ?
(In summary, as the membranes in the 'dome ' part of the injection pump got fractured, so too did the richness control of the engine and difficulty hot starting was the the 'creeping' indicator. r's mike