I am inclined to think GG is correct.
That said I would expect if you stand your ground they company will back down if they can do so.
If you had not gone on maternity leave, would you have been moved anyway ? If so then the terms are no less favourable than had you not gone on maternity leave. It does not say, terms no less favourable than you enjoyed before you went on maternity leave. They are not the same thing.You’re entitled to come back from maternity leave on terms no less favourable than those you would have enjoyed had you not gone on maternity leave.
That said I would expect if you stand your ground they company will back down if they can do so.