Dorothy's income tax and Class 4 NICs liability for 2022-23 was £24,600, of which £600 was deducted at source. Her liability for 2023-24 is £28,000, of which none is deducted at source. She makes a first POA in respect of 2023-24 on 27 February 2024 and a second POA on 12 September 2024. She makes a balancing payment for the year on 21 February 2025. All of her payments are for the correct amount.

(a) Calculate the late payment penalties payable by Dorothy in relation to 2023-24.

(b) Assuming an interest rate of 6.75% per annum, calculate the amount of any interest payable by Dorothy in relation to 2023-24.