Super-Kleer is my fining of choice. The positive/negative combo works on just about anything. Started using it on meads, but use it on beers that need it. Pricy, but it works wonders. Chilling/time can still help, though, especially getting it to pack down to minimize racking loss. It's gravity that's doing the work.
I'd be more concerned about Maris Otter not clearing. You might want to switch maltsters or lots. Crisp MO clears bright for me every time. OTOH, I've had bags of Munton's MO that never clear. Life's too short to use crappy grain. You might also want to check your mash pH, calcium levels, and mash rests. All those can impact clarity. As can your breaks, and how you deal with them. Plus your yeast selection. Poor clarity can be caused by many things; not all fining agents will help, depending on the cause.
Gelatin is better suited to lagers due to temperature. Not surprising it didn't help.