Transparency International director says the findings present a ‘serious issue about exerting influence at the heart of politics’

The Labour front bench has accepted over £600,000 of research help from the multinational accountancy company PricewaterhouseCoopers to help form policy on tax, business and welfare, analysis by the Guardian reveals.

The support to shadow ministers including Ed Balls, Chuka Umunna and Tristram Hunt comes after the Guardian revealed PwC’s role in establishing potentially favourable tax structures for hundreds of companies around the world – including many British businesses – in Luxembourg.

Such arrangements, though entirely legal, have been criticised by politicians from all three major parties as depriving the exchequer of billions in much-needed revenue. Just last year, Ed Miliband vowed to tackle such schemes, warning businesses that “politicians – not companies – set the rules”.

However, during that same period, shadow chancellor Ed Balls received almost £200,000 of secondments from PwC, while the rest of the shadow treasury received over £170,000 worth of support. According to declarations to parliament, PwC analysts provided support “during the passage of the Finance Bill” – legislation which included key anti-tax avoidance measures.

PwC analysts provided specific support to the shadow treasury team for finance legislation passed last year. The Finance Act 2013 included new general anti-tax avoidance rules and a reduction in corporation tax. Both changes impact the accounting firm’s clients and, in a news alert published by the firm the day the act was enacted, it warned US multinational companies to consider the consequences of the new regulations.

It has been a longstanding, if not greatly publicised, practice in Westminster for opposition parties to receive support from the major accountancy companies in formulating their policies, particularly ahead of general elections.

Last year the influential public accounts committee highlighted examples where employees from big four accountancy firms that are advising government “go back to their firms and advise their clients on how they can use those laws to reduce the amount of tax they pay”.

When asked about the relationship between the opposition frontbench and these firms, Margaret Hodge, the Labour chair of the committee said: “The issues the Guardian raises are very important. Any politician who accepts support in kind or financial support must consider thoroughly all conflicts.”

Since 2010 PwC staff have held positions in the offices of shadow ministers of international development, business and education. A senior associate at the firm, Thomas Graham, is currently on a six month posting worth £75,000 to shadow education secretary Tristram Hunt.

Shadow business secretary Chuka Umunna had research support from PwC between September 2013 and January 2014, and again between June and September this year, with a total value in excess of £60,000.

A spokesperson for the Labour party defended what they characterised as “long standing support to all three major political parties on a non-party basis” from accountancy firms and said seconded staff “do not influence opposition policy decisions.”

“Given the complexity of government decisions in areas such as tax policy – and that opposition parties do not have significant access to civil servants – the support provided by organisations such as these helps ensure that there is better scrutiny of government policy.”

The party did not respond to questions regarding PwC’s role in setting up Luxembourg structures, or any specific measures taken to prevent PwC or its clients benefiting from their staff’s position advising frontbenchers.

Analysis of the Electoral Commission’s register of donations shows Labour has also received over £250,000 worth of staff costs from KPMG, another of the so called “big four” accountancy firms, which between them conduct most of the audit work for the world’s largest corporations.

Unlike the PwC secondments to the front bench, KPMG staff are not included in parliamentary registers, as the support was not provided directly to MPs’ offices, but to party headquarters.

Robert Barrington, the executive director of Transparency International, said the Guardian’s findings highlight “the huge gap between regulations on the revolving door, lobbying and political donations and what actually happens in practice.”

“There is a serious issue about the ability of professional firms to exert influence at the heart of politics, with the danger that policy-making by government and opposition parties is contracted out to well-resourced entities with a significant vested interest.”

Professor Sikka, a professor of accounting at the University of Essex, challenged the dominance of accountancy companies in giving advice.

“Labour argues these firms are providing valuable technical advice,” he said, “but there are plenty of non-commercial others who can provide technical expertise and isn’t it about time they got some expertise of their own?”

The Guardian analysis shows that since the last election – when support was going to the Conservatives, rather than Labour – PwC has come to dominate shadow ministerial offices to a far greater extent than any of its major rivals.

Since entering government, the Liberal Democrats have received over £500,000 worth of staff costs from PwC and KPMG combined. Between 2005 and 2010, the Conservatives received secondments worth £1.5m from the big four accountancy firms as well as large US firms, Boston Consulting and Bain & Company.

The Guardian’s revelations in the Luxembourg Files raise further questions as to Luxembourg’s role in facilitating legal tax avoidance, for which it has already come under criticism from other EU leaders, as well as the role of firms such as PwC in facilitating these favourable deals.

PricewaterhouseCoopers said it had a “clearly stated” policy on political engagement, saying it had “no political affiliation” but rather sought to maintain “constructive relations” with parties “in the interests of the firm and its clients”.

“Our people provide limited and fully disclosed technical support to the main political parties in areas where our expertise and knowledge of the business environment can help them better understand technical matters and the consequences of their policy proposals,” PwC said in a statement. “We do not develop policy on their behalf.”

PwC said last week, in response to the ICIJ/Guardian revelations from Luxembourg, that questions were based on “outdated” and “stolen” information, “the theft of which is in the hands of the relevant authorities”.

KPMG said its secondments to political parties were a “longstanding policy”.

“When staff are seconded, they operate entirely under the direction and management of the relevant party and the secondments are underpinned by strict confidentiality agreements,” the company said. “As such, KPMG receives no benefits or favourable treatment.”