Two of Britain's largest lobbying firms have launched bids to help big business exploit the European Citizens' Initiative – a new programme that was meant to involve ordinary people in EU law-making, The Independent has learned.

A leaked memo shows that Bell Pottinger, the subject of an undercover investigation published in this newspaper in December last year, has offered to help potential clients set up petitions demanding changes to EU law under the new programme, whose rules specifically bar organisations from doing so.

And information posted on the website of its fellow lobbyist Fleishman-Hillard shows it too is offering to help businesses hijack the initiative, which came into force on 1 April.

"They are trying to muscle in. We have done everything we can to try to put safeguards in place to discourage that from happening," said an aide to Maros Sefcovic, the European Commission's vice-president, who is responsible for setting up the initiative.

The revelations will put more pressure on David Cameron to take action over lobbying firms based in Britain. In February 2010, he made a speech warning that lobbying in Westminster was "an issue that exposes the far-too-cosy relationship between politics, government, business and money".

Plans to introduce a register of lobbyists, potentially forcing firms to reveal client lists, were announced by the Government in its Coalition Agreement. A consultation, due to close this week, will look at who will be compelled to sign. But, under the current terms set out by the UK Public Affairs Council, companies based in Britain but lobbying in Brussels are not defined as lobbyists. Tamasin Cave, director of SpinWatch and leader of the Alliance for Lobbying Transparency, said: "Professional lobbyists already have such disproportionate access to Brussels. If they are seeking to use the European Citizens' Initiative [ECI] to gain more influence, it does not seem to be in its spirit; it almost seems greedy for them to try to muscle in.

"The ECI is about grassroots initiatives. They [the lobbying industry] will seek every opportunity to get the private interests of their clients in front of legislators and to gain more access to the corridors of power in Brussels."

The ECI was devised as a way of bringing the European Union's citizens closer to its law-makers. Under the Initiative, petitions which attract one million signatures or more will be considered as possible laws. The petitions can be set up by a group of EU citizens who must live in at least seven different countries between them and be old enough to vote.

The rules governing the scheme state: "Citizens' initiatives cannot be run by organisations." Organisations are not barred from promoting or supporting existing petitions, "provided that they do so with full transparency".

But, in an email, sent by Bell Pottinger's director of European affairs Daniel Hamilton and seen by The Independent, the firm said: "The ECI provides an exciting opportunity for businesses and campaign groups directly to influence EU policy and their profile across the organisation's 28 member states ... Organisations interested in deploying citizens' initiatives will need to have substantial resources and support both at a grassroots and professional level.

"Bell Pottinger Public Affairs can provide that professional support, guiding you through the process of devising, launching and managing an initiative..."

And, on its website, Fleishman-Hillard claimed: "the ECI is not a tool reserved for NGOs; corporations can use it too," adding later: "[our] team of seasoned public affairs and online communication professionals can help you monitor emerging ECIs, assess their potential impact, and support you in launching your own ECI ... We are well-placed to assist your organisation in rolling out pan-European grassroots campaigns..."

David Babbs, director of 38 Degrees, which has campaigned against lobbying in Westminster, said: "This is a really murky world. In serving clients' interests, lobbying firms will be as creative as possible in furthering the agenda of whatever business has hired them."

Fleishman-Hillard told The Independent the aim of its website briefing was to clarify the "practicalities of how a petition could be created according to the European Commission's rules. This advice would not extend to organising citizens' initiatives as this is not in line with the rules". A spokesman said last night that the company would alter its website to make this clearer.