Sir Keir Starmer is alleged to have broken parliamentary rules by failing to declare donations of clothing for his wife Victoria Starmer.
The gifts, from prominent Labour donor Lord Alli, were not initially declared in the register of MPs’ interests.
The Sunday Times reported that the UK prime minister approached the parliamentary authorities on Tuesday to make a late declaration after being given updated advice on what needed to be registered.
The Tories demanded a full investigation into the Starmers’ links with prominent Labour donor Lord Alli.
The Sunday Times reported the donations covered the cost of a personal shopper, clothes and alterations for Lady Starmer both before and after Labour’s election win in July.
MPs are required to register gifts and donations within 28 days.
A No 10 spokeswoman said: “We sought advice from the authorities on coming to office.
“We believed we had been compliant, however, following further interrogation this month, we have declared further items.”
The guide to the Commons rules states MPs should register “any benefit given to any third party, whether or not this accompanied a benefit for him or her, if the Member is aware, or could reasonably be expected to be aware, of the benefit and that it was given because of his or her membership of the House or parliamentary or political activities”.
Lord Alli’s involvement with the Labour leader has already proved controversial after it emerged he had been given a Downing Street security pass without apparently having a government role.
The row was dubbed the “passes for glasses” affair because Lord Alli has previously donated tens of thousands of pounds worth of clothing, accommodation and “multiple pairs” of spectacles to the Labour leader.
A Conservative Party spokesman said: “It’s taken just 10 weeks for Keir Starmer to face an investigation for his conduct.
“After facing allegations of cronyism and now apparent serious breaches of parliamentary rules, there must be a full investigation into the passes for glasses scandal.
“No doubt the millions of vulnerable pensioners across the country who face choosing between heating and eating would jump at the chance for free clothes just to keep warm in the face of Labour’s cruel cut.”
