It is ironic that David Cameron finds himself at the centre of a lobbying row, having warned in 2010 that the business of seeking to influence government was “the next big scandal waiting to happen”.

Ministers and senior officials have been dragged into the row over Greensill Capital’s links with the Government and the former prime minister’s lobbying for the collapsed financial firm.

But what is lobbying, what are the rules, and why does it cause such unease?

– What is lobbying?

Essentially it covers efforts by individuals, charities, organisations, pressure groups and businesses to influence government policy.

This can happen in many ways, from writing to MPs to taking ministers out for dinner and bending their ear about a subject close to your heart – or wallet.

Lobbying can be used to ensure that an organisation’s expert knowledge of a subject is taken into consideration by MPs and ministers as they make decisions about laws or policies.

But it gets into murkier waters when organisations are lobbying explicitly to secure a financial advantage.

– What are the rules?

The Transparency of Lobbying, Non-Party Campaigning and Trade Union Administration Act 2014 makes it an offence for someone who is not a registered lobbyist to directly lobby ministers or senior civil servants.

The legislation, passed by Mr Cameron’s government in 2014, introduced the Registrar of Consultant Lobbyists, which intends to enhance the transparency of those seeking to lobby ministers on behalf of a third party.

Cheltenham Literature Festival
David Cameron (Jacob King/PA)

But people lobbying on behalf of their own organisation are not required to register, which is why the former prime minister was cleared of breaking lobbying rules by the watchdog last month.

– Are there rules for parliamentarians?

The code of conduct for MPs and peers sets out the standards of behaviour expected, including rules concerning additional income, gifts and personal interests that must be declared and published.

Separately, the ministerial code requires ministers to disclose their interests in detail, while the Government publishes information on ministers’ and special advisers’ meetings with external organisations on a quarterly basis.

– What about those leaving Government?

The Advisory Committee on Business Appointments (Acoba) gives advice to ministers and senior officials on avoiding conflicts of interest and whether new jobs comply with the “business appointment rules”.

Former ministers and senior civil servants are expected to seek advice from Acoba about any new roles taken within two years of leaving office. However, the committee has no means to enforce the rules.

This has lead to the committee being branded “totally toothless”, while its role has come under scrutiny in recent days after it emerged a senior civil servant took a role at Greensill Capital while still working in Whitehall.

– What have critics said?

Labour wants to create an “anti-sleaze” committee to investigate lobbying, including the former prime minister’s activities, which would be able to summon witnesses to answer questions in public.

If MPs approve the motion on Wednesday, the cross-party committee would investigate whether current laws are sufficient to prevent “inappropriate lobbying” of ministers and officials.

Senior Opposition figure Rachel Reeves, shadow chancellor of the Duchy of Lancaster, said: “This is much wider than just about what David Cameron has done – this is about what is happening at the heart of Government today.

“This really matters, we need answers, and MPs have a chance to vote for a proper inquiry today.”