Slow worms start to mate around April and May, but cannot actually conceive until June when the females' eggs pass into their oviducts. Although territorial disputes between males are usually settled by scent, occasionally they will fight with each other for possession of females.

Are slow worms aggressive?

Slow worms emerge from hibernation around March with the males appearing first. Slow worms are harmless to humans, but during courtship, male slow worms can exhibit some extremely aggressive behaviour, not only towards other male slow worms, but to females as well, and I suspect this is what you have witnessed here.

Can slow worms live if cut in half?

If an earthworm is split in two, it will not become two new worms. The head of the worm may survive and regenerate its tail if the animal is cut behind the clitellum. But the original tail of the worm will not be able to grow a new head (or the rest of its vital organs), and will instead die.