Keir Starmer is under investigation by the Parliamentary Commissioner for Standards over potential breaches of rules on earnings and gifts.
The Labour leader is being probed by Kathryn Stone over whether he broke two sections of the MPs’ code of conduct on registering interests on employment and earnings.
Stone is also looking at whether Starmer potentially breached rules in the section regarding gifts, benefits and hospitality from UK sources.
Asked about the issue on Monday, the Labour said he was confident he had not broken the MPs’ code of conduct.
“My office is dealing with it and will be replying in due course,” he told reporters while on a visit to Wakefield ahead of the by-election.
Asked if he was sure he had done nothing wrong, he said: “Absolutely confident, there’s no problem here.”