Re the bit about different salaries for the same job.
There is nothing illegal about paying two people different salaries for the same job, as long as it is not below the national minimum wage. This is why some employers have the 'Do not discuss your salary with other members of staff' statement in the contract of employment, some of which go as far as warning of dismissal if you do.
A Company will pay the lowest salary they can get away with, for any employee, regardless of the job they do.