40% tax rate breached by year end bonus

My base salary is under the £50,270 threshold however in my March salary I will get a bonus that will trip me over this threshold by £200! I assume I will get taxed 40% on anything over the £50270 in my March payslip but will this change my tax code from 1257L for next year? I am not guaranteed this bonus next year so my base salary in April will again be under the £50270. This will also mean I am limited to £600 tax free interest in 23\24 before I pay tax on it. I am registered for self assessment so will I be able to complete a self assessment return IF I receive more than £600 interest or will this affect my tax code. Again, no guarantee I’ll be getting any interest next year as funds will be spent soon on a property!

Hi

While you will be due to pay 40% tax on any income above £50,000, this should not affect your tax code.
You should still be able to complete a tax return and pay any amount due via Self Assessment. 

Thank you