Receiving large gift, tax and plan implications.

Hello if my parent was to gift me £1m then died in the next 5 years i would have to pay the corresponding tax bracket for that range. Correct? If i blow 1m and tax man comes knocking does that mean i am now in debt to the tax man? If i was to put aside £1m..essentially lock it up so i can make sure i can cover any taxes wheres the best place to lock it up near risk free but still assume interest? Just a fixed savings account?