I have just been acting for my father - first as Deputy in the Court of Protection ( a bit like having power of attorney) and then as joint executor. The banks and investments would not shell out a penny, except for the funeral costs, until we had probate. That took nine months. Until then, everything was locked solid. Death certificates were produced to all banks and investment organisations, building society, Premium Bonds etc, and it was months before even the cheque account was transferred to the executors. Then that involved closing the old account and opening a new one in the executors' names.
Life insurances would pay out, yes. Some other policies, perhaps. But only if there were an account jointly in the names of the deceased and the deceased's spouse would the survivor be able to lay hands on the money in that account. And I have never heard of it being paid out in the form of a single cheque. The account would first have to be changed from "mr and Mrs Bloggs " to "Mrs Bloggs" and a new cheque book issued.
Even so, what about the will ? I don't believe cheques can be made out for amounts like that to anyone except executors, and then only after probate has been granted.
This business of several large payouts by cheque does not sound remotely like standard UK bank practice to me.