LEGAL: How can you remove squatters from a building?

The owner of the building has found squatters have moved in and one of them was injured, can the injured party issue a claim against the owner of the building?

Potentially, yes. If the building was unsafe. The owner owes a duty of care to those who enter the land even illegally, though the duty is lower in that regard.

In terms of removal you need a court order. Alternatively, if they leave you secure the property. A forced entry will be responded to by the police as a criminal matter and the police should remove them.