Interest Rate for outstanding tax payment

I would like to know what interest rate applied if my actual tax payment is higher than the advanced tax payment? e.g. If I pay 500GBP for my advanced tax payment for 2024-25, the actual required tax payment is 600GBP, I need to pay 100 GBP outstanding tax payment and do I need to pay the interest related to this 100GBP tax payment?

Hi,
If the remaining balance of £100 is paid by the due for 2024 to 2025 tax year of 31 January 2026 then no interest would be charged. 
Thank you