Keir Starmer has been found to have breached the MPs’ code of conduct by failing to register on time eight interests, including gifts from football teams and the sale of a plot of land.

An inquiry into the Labour leader was opened in June by the parliamentary standards commissioner, Kathryn Stone, relating to claims about late declaration of earnings and gifts, benefits or hospitality from UK sources.

Speaking at the time, Starmer said he was “absolutely confident” he had not broken the MPs’ code of conduct.

The commissioner has now found that leader of the opposition failed to register eight interests – five more than alleged in the original complaint.

However, she noted the “breaches were minor and/or inadvertent, and that there was no deliberate attempt to mislead”.

The watchdog therefore decided the inquiry could be concluded by way of the “rectification” procedure, without a referral to the committee on standards, which happens in more serious cases. The rectification procedure entails publishing the details and an apology on the House of Commons website.

A Labour party spokesperson said: “Keir Starmer takes his responsibilities to the register very seriously and has apologised to the commissioner for this inadvertent error. He has assured the commissioner that his office processes have been reviewed to ensure this doesn’t happen again.”

In the original complaint made to the commissioner, it was alleged that between 6 March and 13 May 2022, Starmer had failed on three occasions to register income and hospitality that he had accepted within the 28-day deadline set by the house.

The watchdog undertook a review of Starmer’s register entry over the last 12 months and noted four additional late entries.

During the investigation, Starmer also informed Stone he was in the process of selling a plot of land for a sum that exceeded the £100,000 threshold for registration set by the house.

Stone found Starmer had failed to register the eight interests, including the plot of land, and “had breached paragraph 14 of the House of Commons’ code of conduct for members of parliament”.

However, she went on: “I found that, based on the information available to me, the breaches were minor and/or inadvertent, and that there was no deliberate attempt to mislead.

“I decided, therefore, the inquiry could be concluded by way of the rectification 35 procedure available to me under Standing Order No 150.”

Starmer received an £18,450 advance from publisher HarperCollins in April for a book he is writing, in which he is expected to set out his vision for Britain.

The sum – which he has pledged to donate to charitable causes – was declared a day late, while declarations of royalties for two legal books published before he became an MP were also delayed.

Starmer also received use of a directors’ box for two people at Crystal Palace football club – worth £720 – when the team thrashed the club he supports, Arsenal, 3-0 on 4 April. It was not registered until 5 May.

He received four tickets for Watford v Arsenal, worth a total of £1,416, for their 6 March match. The gift was registered on 6 May.

Just Eat also gave tickets to his staff for the Taste of London festival and the British Kebab awards. The donations from the company exceeded the £300 limit for registration on 29 October but were not declared until 23 December.