1. You can give up your right to an inheritance. What you would have received then goes to the other beneficiaries under the terms of the will. As you have not received anything you have no tax liability.
2. It is the duty of the executors of the will to determine the assets and debts of the estate, pay any inheritance (or other) tax due, obtain probate and distribute the estate to the beneficiaries.
So if - and it seems very unusual - you don't know about the inheritance for 5 years, the executors should already have paid any inheritance tax. The tax is based on the value of the estate as at the date of death. It (or much of it) has to be paid before probate can be obtained, or else arrangements made with HMRC to pay it (with interest added) over a period. I am not aware of penalties for delay, but there may be some.
It is possible there are no assets in the estate sufficient to pay the inheritance tax other than the house. If this is the case, the executors should discuss what is to be done with the beneficiary who has been left the house. It may have to be sold, or the beneficiary may have to raise a mortgage on it to pay the tax.