At the present your overpayment should but see later remove £3000 from the debt. This will reduce payments by £3000 x 0.0589 per annum divided by 12 for monthly. However beware since some Mortgage Suppliers see overpayments on Interest Only, as reducing the Interest element by that amount only. It is suggested you ask them whether the first option holds in that the Principal is reduced as Interest Only mortgages sometimes hold the Capital as fixed over the term, then any payment normal, or overpayment is put against Interest. Check this carefully before doing anything.

Ask your provider

By my rough check it will knock about 5% off of your monthly payment. But make sure that you policy allows one of lump sum payments, you may get charged for the privellige