If the options listed above aren’t affordable, you need to contact your lender as soon as possible to discuss your situation. They'll be able to work with you to try to come to a manageable solution.
A more drastic solution would be to sell your property and buy a smaller one to release funds to cover the shortfall. This is a last resort for many people and there are no guarantees that you will sell your home for a price you expect or find a cheaper property that you want to live in.
Finally, if you’re 55 or over, you could consider an equity release scheme, such as a lifetime mortgage or home reversion plan. These are complex products that enable you to release equity tied up in your home while continuing to live in it.
However, they will affect the amount you leave in any inheritance, so it’s important to get independent financial and legal advice before deciding.