David Cameron said he is confident his party can answer allegations it broke electoral laws during last year's general election campaign.
But the Prime Minister said if there were "misdeclarations or things left out" from its spending accounts then the Conservative Party must put them in place.
The party faces multiple police investigations as well as a probe by the Electoral Commission over allegations the Tories breached spending rules ahead of their knife-edge poll win last year.
They centre on whether the Tories should have listed the costs of bussing activists into key marginal seats under local spending accounts, rather than its national spending budget, which was larger.
The Prime Minister told ITV's Peston on Sunday: "In the end I'm responsible for everything. But I'm very confident that the Conservative Party is gripping this, with the chairman Andrew Feldman (Lord Feldman).
"Lots of political parties have these bus tours, buses that go round different constituencies, and that is a national expense.
"This is all now in conversation with the Electoral Commission and these other investigations so we should let that take its place.
"But I'm confident, the idea of a bus that is a national bus that visits constituencies, I think the Labour Party's done that, the Liberals have done it, we've done it..."
He added: "I don't believe we have done anything wrong. If there were misdeclarations or things left out we have to put those in place but I'm confident we can answer all the questions being put to us."