Should the questioner demand the full amount from his friend (150,0 pounds + 50,0 pounds in profit), or only the principal amount (150,0 pounds), knowing that the friend squandered the money and did not achieve the agreed-upon profits?

If the aforementioned agreement guarantees a specific profit for the mudarib (investor/agent), then this is a corrupt contract considered a usurious loan. Guaranteeing the principal in mudarabah (profit-sharing partnership) invalidates it by consensus. Since the mudarib did not use the money for its intended purpose but spent it on himself, he is liable for it to its owner, and he is not permitted to take anything beyond the principal. The questioner must return only the principal to the owner of the money, without the aforementioned profit.