Hello again, just to confirm you are on maternity leave now and this new job is a potential opportunity for when you return from ML?
If a redundancy situation arises during your maternity leave and the employer cannot employ you under your existing contract, you are entitled to be offered a suitable alternative vacancy (where one is available) to start immediately after your existing contract ends.
The new contract offered must be such that:
This effectively means that you get priority over any other employees at risk and the employer must actually be offered the job before they are considered for it. Your old job may no longer exist but the employer has to consider anything else that is available and offer it to you first, meaning you have first refusal over it and only then can they consider others for it too.
You can certainly go through the grievance procedure if it does not appear you are getting anywhere with the current attempts of trying to resolve this. You cannot choose who deals with it and whilst the initial grievance may be dealt with by your manager or someone currently involved in the process, you can appeal the decision and that should then go to someone more neutral for a second opinion.