A leading Labour MP has been reported to parliamentary authorities over an undisclosed interest in a "wealth management" company catering to rich non-doms and offshore clients.

Records at Companies House, independently corroborated by BuzzFeed News, show that Gisela Stuart, chair of the Vote Leave campaign to take Britain out of the EU, inherited a partnership interest – equivalent to a shareholding – in Vestra Wealth LLP in 2012 from her late husband.

The company, which was co-founded by Stuart's husband, offers "tax planning" to "high-net-worth" and "ultra-high-net-worth" clients, including UK-based non-doms, who enjoy significant tax advantages compared with most UK citizens.

In 2015, while holding her stake in Vestra, Stuart ran unsuccessfully to become chair of the influential Commons public accounts committee, promising in her manifesto to focus on "an effective tax system that delivers; eliminates aggressive avoidance, and establishes clear rules which are properly enforced".

Her stake was uncovered by journalist Martin Williams during his research for the book Parliament Ltd: A Journey to the Dark Heart of British Politics, which is published on Thursday.

When Williams discovered the stake in January, it was not declared on Stuart's entry in the register of members' interests, a public list on which MPs are required to disclose outside employment and significant shareholdings, to avoid any undisclosed conflicts of interest.

Asked about the company by Williams on 25 January, Stuart said: "Essentially, it invests serious[ly] rich people’s money ... this is the first time anybody’s ever mentioned it."

Stuart's entry on the register of members' interests was then updated on 27 January to include her Vestra Wealth stake for the first time. The section for including shareholdings worth "over £70,000" now states:

Vestra Wealth LLP; a private wealth management company. This interest

achieved registrable value on 25 January 2016. (Registered 27 January

2016)

Asked about the apparent coincidence of her Vestra Wealth stake becoming of registrable value on the same day Williams spoke to her about it, she told BuzzFeed News that she had only checked the value of her stake after being questioned.

"I inherited the interest as part of my husband’s estate when he died in 2012," she said. "The probate value was below the level required for registration.

"Following Mr Williams' visit I asked for an updated valuation and was provided with a valuation. As a private partnership there is no regular valuation of the business as any such valuations are only carried out if there is a particular purpose such as death or sale or purchase of interests. I then immediately registered the interest as required."