Mortgage amount to be repaid: Why so high?

My partner and I are taking a mortgage for a house costing £270,000. The mortgage offer states that the total repayment amount over the term is approximately £688,900, which equates to paying £2.84 for every £1 borrowed.

Here are the details:

We’re putting down a 10% deposit, so we’re borrowing £243,000.

The loan term is 40 years.

The interest rate is fixed at 4.92% for the first two years.

This £2.84 per £1 borrowed seems excessive to me. Am I missing something here?

When I used an online amortization calculator, I estimated £320,000 in interest, plus the £243,000 capital, giving a total repayment of about £550,000—significantly lower than the £688,900 mentioned by the bank.

However, the offer also mentions an APRC (Annual Percentage Rate of Charge) of 6.6%. When I input this into the calculator, I got a figure closer to the bank's estimate of £688,900.

Interestingly, the offer notes that the APRC is calculated "using assumptions regarding the interest rate." Could this explain the discrepancy?

This is the exact wording in the offer:

"Main features of the loan Amount and currency of the loan to be granted: £242,550.00 Duration of the loan: 40 years This is a repayment loan of £242,550.00 on a fixed rate that will apply from completion until 31 March 2027. After 31 March 2027 the rate that will apply is a variable rate, which varies in accordance with changes to the Bank of England Base Rate. The variable rate will not go below a floor for the remaining term The Bank of England Base Rate is a variable rate set by the Bank of England. For further information please visit www.bankofengland.co.uk. Total amount to be repaid: £688,871.85. This amount is illustrative and may vary, in particular in relation with the variation in the borrowing rate. This means that you will pay back £2.84 for every £1 borrowed. The purchase price of the property assumed to prepare this Offer: £269,500.00 could theoretically borrow on this loan would be £242,550.00 Maximum available loan amount relative to the value of the property 90.00%. The maximum amount you This loan is secured on your home. "

And in the next page: "The APRC is provided to help you to compare different offers. The APRC applicable to your loan is 6.6% It comprises: Interest rate(s) Step 1: A loan of £242,550.00 on a fixed rate of 4.92% that will apply from completion until 31 March 2027. Step 2: After 31 March 2027 the rate that will apply is a variable rate, which is 1.99% above the Bank of England Base Rate, currently 4.75%o, to give a current rate payable of 6.74%. The variable rate will not go below a floor of 1.99%, for the remaining term."