You then have to pay the interest on that mortgage on a monthly basis for as long as you have the mortgage.
As they are interest only you only pay the interest each month, none of the capital, so the amount you owe remains constant over time.
You can pay off the mortgage at a later stage e.g. when you receive a pension payout, encash another investment or if you sell the property.
We can refer you to a recommended and experienced broker who can pass detailed illustrations for the schemes that are available so that you can fully understand the terms and conditions.