Quaid-e-Azam

Another thing to note is that all biographical accounts refer to Jinnah’s family members with the surname of ‘Jinnah’ and not ‘Jinnahbhai’. This is quite unusual, as the children of Jinnahbhai Poonja would have been likely to keep the name of their father, but it seems that they all came to be known with the surname of ‘Jinnah’ thereafter..
Now, the key piece of information, from which I extrapolate this theory, comes from Fatima Jinnah’s book ‘My Brother’ and various other biographical accounts. These mention that towards the end of young Jinnah’s time in England, he received letters from his father to inform him of his mother’s death, as well as the fact that the family was in financial ruin. Jinnahbhai Poonja’s thriving business had gone up in flames. Fatima Jinnah goes on to say that during this time of financial turmoil, Jinnahbhai Poonja had began “trading” in the name of her brother (i.e. Mahomedalli Jinnahbhai). This is the main item to highlight.
What most likely happened here is that the ‘company’ established in the name of Mahomedalli Jinnahbhai accumulated an enormous financial burden and its wealth was likely subject to litigation due to Jinnahbhai Poonja’s previous failures.