Your funeral expenses and any other debts outstanding at the time of your death e.g. bills, loans, mortgages can be offset against your estate for Inheritance Tax calculations.
Expenses incurred after death e.g. Probate fees, professional help with probate (solicitors, financial advisers, accountants), inheritance tax, estate accounts, tax returns and self assessment help cannot be offset against inheritance tax.
Why? Because if you were alive you would not be incurring these expenses but these same expenses can still be refunded to executors out of the estate (after taxes) and before net estate distribution.