Your monthly payments will be higher for the next 12 months. Then they’ll go back to what they were before.
Here's an example of how this would work:
John’s 3 month payment break
John took a 3 month payment break. He has a repayment mortgage of £160,000 on an interest rate of 4.00% and has 24 years and 1 month left on his mortgage. His monthly payment before he took a payment break was £863.32 each month.
After a 3 month payment break, John decided to repay the agreed missed payments and interest over 12 months. His new monthly mortgage payments for 12 months were now £1083.85 an increase of £220.53 each month. Overall John will pay £56.40 in additional interest over the 12 month period. After 12 months Johns payments go back to what they were before and his remaining mortgage term won’t change.