A grant of probate is a court order giving the executor the right to carry out the wishes expressed in the will. Unless the estate is very small, banks and other institutions holding assets of the deceased will not hand those assets over to the executor until a grant of probate is produced.
If assets are jointly owned, then probate may not be necessary. In many husband/wife situations, the family home is jointly owned and the parties have joint bank accounts. If you are named as an executor of a will, it is wise to seek legal advice as to whether a grant of probate is necessary. In small estates, even if assets are held in the name of the deceased alone, it is sometimes possible to administer the estate without the need to apply for probate.

