Senior members of the Shadow Cabinet have been accused of potential conflicts of interest after their offices were shown to be funded by companies that have direct interests in their policy portfolios.

A report by the Parliamentary Standards Commissioner revealed the office of shadow Housing minister received support from five companies including an estate agent and two mortgage brokers, while a medical equipment company's former boss gave money to fund the office of shadow Health Secretary, Andrew Lansley. The money was channelled to run their offices by Conservative headquarters, declared to the Electoral Commission but not placed on the Commons Register of Members' Interests.

Grant Shapps, the housing spokesman, has been revealed as the recipient of tens of thousands of pounds in cash from five companies linked to his portfolio. And Jeremy Hunt, the shadow Secretary for Culture, Media and Sport – whose brief includes tourism – took funds from the chairman of the Conservative Tourism Taskforce, John Lewis, who is also former chairman of the British Tourist Authority.

Alan Duncan, the shadow Business, Enterprise and Regulatory Reform Secretary, received funds from the president and chief executive of the oil company Vitol, Ian Taylor, who is a former colleague of Mr Duncan's and runs a company which used to employ Mr Duncan as a consultant.

Labour went on the offensive, accusing the Conservatives of concealing potential conflicts of interest. But the Tories said it was "utter nonsense" to accuse them of any conflict, insisting they had volunteered information about donations channelled to frontbenchers by party headquarters to fund Shadow Cabinet offices.

The Commons committee formally upheld a complaint against George Osborne, the shadow Chancellor, for failing to declare money in the Commons register of interests that had been raised by Conservative Campaign HQ. But the Parliamentary Standards Commissioner, John Lyon, said it would not be "fair and reasonable" to criticise Mr Osborne over the failure as the party chiefs had sought official advice on the issue and "acted in good faith" in interpreting it. Mr Lyon said it was "a story of misunderstandings, of discussions held at cross purposes, of the misinterpretation of conversations and emails".

Other members declaring donations included David Davis, the shadow Home Secretary, Peter Ainsworth, the shadow Environment Secretary and Michael Gove, the shadow Children's Secretary.

The Labour MP Kevan Jones, one of those who made the complaint, said: "David Cameron lectures others on transparency, he should now... publish a full list of those buying influence in his party."

Tories in trouble

George Osborne

The shadow Chancellor was found to have broken the rules by failing to declare £500,000 which had been channelled through Tory HQ from donors to run his office.

Alan Duncan

The shadow Business Secretary received funds from Ian Taylor, the president and chief executive of Vitol oil company, who is a former colleague of Mr Duncan.

Grant Shapps

The housing spokesman took tens of thousands of pounds in cash from five companies linked to his portfolio.

Andrew Lansley

The shadow Health Secretary received funds from London Secure Services and Julian Schild, who owned a medical equipment company, Huntleigh Technology, the largest manufacturer of NHS beds, until last year.

Jeremy Hunt

The shadow Culture Secretary, whose brief includes tourism, received funds from the chairman of the Conservative Tourism Taskforce, John Lewis, also a former chairman of the British Tourism Authority.