The consequence for not seeking leave where a ground of appeal is of mixed law and fact is fatal to the ground. However, one ground of appeal on law in a Notice of Appeal, I must observe, is capable of sustaining an appeal but not otherwise in which case the Notice of Appeal as well as the grounds of appeal is incompetent and liable to be struck out. – Chukwuma-Eneh JSC. Yaro v. Arewa CL (2007)
Now, any party to an appeal who seeks the determination of an issue that was never raised at and determined by the trial and/or lower Court must show that it has sought and obtained the leave of the Court earlier. It is long settled that where no leave was sought and obtained, and one is required, the appeal is incompetent and liable to be struck out. See EHINLANWO V. OKE & ORS (2008) LPELR – 1054 (SC) and METUH V. F.R.N (2017) 4 NWLR (PT 1554) 108 at 121.
— M.D. Muhammad, JSC. Friday Charles v. The State of Lagos (SC.CR/503/2020, Friday March 31 2023)