Hello, my S reg marea 1.9 diesel is having trouble starting in this cold. It's not the battery, brand new and fully charged, I'm new to car maintenance so I hope it's anything but the glow plugs. Any ideas would be helpful

You might get a bit idea here https://www.fiatforum.com/marea/126642-marea-jtd-cold-starting-problem.html I know yours wont be a JTD but thats all I could find in the search.

It may be the fuel, depending on when you last filled up it may not have winter diesel yet.