Vehicles use for work - can I claim milage I havent expensed to employer?

I regularly travel to the local airport when travelling to visit customers for my employer. 50% of the time I take a taxi and that gets expensed. The other 50% of the time I take my personal car, when I do so, I have not claimed any milage. Can I claim that milage on my self assessment? Is it worth it? Potentially its worth £300+. Its about 6+ times a year, 24 miles, and looks like if I can claim via self assessment, it would be current year and previous 4. I have evidence of the trips as I have airport parking email receipts with registration and dates.

Hi,
Please have a look at the guidance on employment expenses at Claim tax relief for your job expenses.  
If you have submitted your 2024 to 2025 tax return, you would need to amend your return to include mileage allowance in tehebox ' Business travel and subsistence expenses' or box 17 of SA102.  
Parking receipt would be declared in the box, Fixed deductions for expenses' or box 18 of SA102.
Thank you.