"The next morning, I invested the ten pence in two large apples. I
spent the entire day polishing them and I sold them at 5pm for twenty
pence. I continued this system for a month. Then Grandma’s father died
and left us two million pounds."
...at which point he would, in theory, have made well over 100 million.
JD 'pedant' B.
[spoiling jokes since 1972]
An then there was the story of the man who claimed to be a self-made
millionaire. He inherited 5 million and turned it into 6 million.
Assuming 100 pence / Pound:
At the end of the 30th day, if he was not stretching the truth, he would
have been polishing those apples at the rate of over 40,000 per second,
around Mach 10.
Those two million pounds from his father-in-law would not be enough to
pay even the income tax on the earnings from the apples.