Acts of cannibalism among common wall lizards are not unusual, but they probably don't occur very frequently in a natural environment. In my experience, the biggest Podarcis muralis males eat pretty much anything they can overwhelm, but in roughly 40 years of observing lizards I've only ever seen one instance of a common wall lizard "doing a Hannibal Lecter" and munching on an individual of its fellow species.
This was in May 2022, and although it was quite shocking to see a lizard eating its own kind, I was very happy to have my camera with me and that I was able to get some footage. And I have to admit: as gruesome as it was to watch this reptile devouring its smaller, aahm.. "mate", I always find it comical when a lizard tries to gulp down something that just doesn't fit (although it DID manage to swallow the other lizard whole in the end, except for its tail, which was just too long and remained there hanging out of its mouth like an oversized tongue as you can see in the last photo).
But I believe unless there's a severe shortage of other prey like snails, worms and insects in their habitat, it is not common practice among our 4 native lizard species to feast upon each other, and even the much bigger western green lizards (Lacerta bilineata) usually behave quite indifferent towards their smaller cousins, and I often find them basking in the sun together.
The scene of cannibalism I captured was very unexpected to me, because I first thought it was a mating ritual. The male grabbed the smaller female by the head and dragged her around for a while, and it looked like he just had her by the wrong end by accident and wanted to mate. But all of a sudden he started biting down on her head viciously and began to swallow her! I only started filming when I realized what was happening, so the beginning is missing, but if you're interested you can watch the film clip here.
Because the female is already twisted in her death struggle she looks smaller than she actually was, and the male is exceptionally big and certainly the "giant" in my garden, so I don't know; I guess it IS possible that this was a mating ritual gone wrong by mistake. After all, these reptiles don't have the biggest brains, and once they have something in their mouths, the impulse to gulp it down might occasionally become stronger than the one to procreate ;-)