Mileage tax relief and car allowance

Hi, I've tried to claim back mileage tax. My employer currently pays me below the 0.45p but I receive a car allowance. My tax code is 1419L which is higher than the standard 1247L. After trying to claim back mileage tax I now owe £400. How do I find out why my tax code is 1419L?

Hi,

You can view the breakdown of your tax code online if you have a personal tax account:

Personal tax account: sign in or set up

Thank you.