The Shadow Education Secretary has said the Charity Commission "should be much tougher" in its public benefit testing for private schools, adding that if Labour were to get into power, it may look at primary legislation measures.

Speaking in an interview with the Guardian Stephen Twigg said that are a "significant number of private schools that are failing to fulfil their charitable objectives" and said there should be a "proper, open, transparent process that is very, very rigorous in how it treats private schools and charitable status".

The Charity Commission is in the middle of a three-month consultation of its new guidance on public benefit. It was forced to re-write its guidance after the Upper Tribunal found that parts of the guidance were "obscure", "ambiguous" or "wrong", when the Independent Schools Council challenged the Commission in court. The tribunal ruled that private schools would not lose their charitable status if they did not fit within the public benefit guidance, but that schools "must provide more than a token public benefit".

The matter of public benefit was one of Lord Hodgson's 13 consultation questions in the recently published Charities Act Review. The Lord concluded that while the Charity Commission's new guidance should be given time to bed-down, the regulator should consider producing "a single piece of guidance setting out how it defines each of the charitable purposes and the factors it will consider when applying those definitions to decide whether an organisation qualifies as charitable".

But Twigg believes that the current reliance on case law and guidance is not enough, and that new legislation may be necessary: "It may be that we need to look at primary legislation on this," he told the Guardian, "And I would do that because it is a serious issue if schools are getting the benefit of charitable status and aren't doing anything to fulfil that benefit." 

He does, however concede that not all private schools are shying away from their responsibilities, referring to Manchester Grammar as an exemplary private school for serving the community at large.

Rudolf Eliott Lockhart, deputy general secretary, Independent Schools Council focused on this note of positivity in responding to Twigg's comments: "It is pleasing to see Stephen Twigg recognise the wide variety of ways independent schools support their broader communities. He cites Manchester Grammar School where their work with local primaries and the city council exemplifies the strong partnerships which exist between so many private and state schools,” he said.

A general election could be anything up to almost three years away, with the deadline sitting at 7 May 2015, but the comments add to wider discontent on the matter of public benefit. Compliance in reporting the public benefit requirement is "very low" according to Lord Hodgson, but a recent survey by Ipsos Mori into public perceptions showed that evidence of impact was very important to 74 per cent of the public.

The Charity Commission had "nothing to add" to Twigg's comments but advised that the most important thing was that people are engaged with the consultation on the revised guidance.