The implication of saying that you need the extra scrutiny is that either the Commons doesn't reflect the will of the people; or that the will of the people is not what ultimately makes law. If the people elect idiots and get bad legislation, that is democracy for you.
Of course, FPTP more-or-less guarantees that the government has a majority in Parliament without having a majority of the vote.
Defenders of FPTP often say that one advantage is that it means that the government has a clear majority. If that were such a good thing, why would we need a second chamber to balance it?
They specifically say that they do not know whether the bank concluded that the expenses were improper.