Firstly, you and your colleagues are not currently under consideration for redundancy (though I appreciate this may change).
Secondly you need to consider what protocols normally apply to job transfers within your workplace (and it does sound like this transfer occured within the same workplace?). In the private/commercial sector there is no way that such transfers get advertised each and every time. I am referring to transfers at the same grade - not transfers on promotion. Are such job opportunities generally always advertised in your work environment? If so, you might reasonably wish to enquire why this one wasn't.
Thirdly I'm not sure what you mean by 'pay protection' unless you mean the job is a lower grade and the successful applicant is subject to the salary being held flat for 3 yrs. One wonders how you know this - every organisation I have ever worked in, such individual arrangements are confidential between the individual and the HR department.
In summary, because of the first point, there is not yet any formal reason for the employer to seek to redeploy staff. I can't be sure about the fairness of the second point. certainly no employment law that I know of has been broken - your route, of course, would be a raise it as a grievance.