Mty father in law has recently passed away, but before doing so advised my mother in law of an ISA that he has been paying into, which contains around �3000. Due to his condition he was unable to sign any documents to transfer control of the account to her. Now that he has died, will control of the account automatically transfer to my mother in law without any complications ?
Depending on whether he left any other assets, it may be necessary to get probate (Will) or Letters of Administration (no will) before assets can be accessed.
If this was just about his only asset the bank may agree to pay without probate, etc.
And control of the account will not actually pass to your mother at all - as it's an ISA it cannot be transferred, and will have to be repaid.