How many hours is legal ?

8.1 You must work with other members of the team to promote health
care environments that are conducive to safe, therapeutic and ethical
practice.
8.2 You must act quickly to protect patients and clients from risk if you
have good reason to believe that you or a colleague, from your own
or another profession, may not be fit to practise for reasons of
conduct, health or competence. You should be aware of the terms of
legislation that offer protection for people who raise concerns about
health and safety issues.
8.3 Where you cannot remedy circumstances in the environment of care
that could jeopardise standards of practice, you must report them to a
senior person with sufficient authority to manage them and also, in
the case of midwifery, to the supervisor of midwives. This must be
supported by a written record.

Each employer should be asking to know about hours worked elsewhere.

The scenario you have mentioned is unprofessional and unsafe, never mind greedy and dangerous...