A report by the campaign group Spinwatch highlights the lobbying clout of consultancies such as Brunswick and Finsbury. It shows how key financial lobbyists have attempted to cultivate relations with London Mayor Boris Johnson.
It also claims to outline lobbying tactics employed by industry bodies such as the British Bankers' Association.
These are said to include 'secret meetings' with ministers and officials and 'private parties' attended by government figures such as Lord Mandelson.
An Inside Job: A Snapshot of Political Schmoozing by the City concludes: 'We currently have no way of knowing what lobbying is under way in relation to banks and the financial sector, and how such lobbying might be harmful to the public interest. Transparency is needed if we're to have government accountability on these issues.'
But BBA assistant director Brian Capon hit back: 'Of course we talk to ministers and other parliamentary officials - that's part of our job and the two-way communication is valuable in establishing a greater understanding between us.
'To suggest these meetings are "secret" simply fuels the media hype that surrounds the issue, which brings us back to the reason why it's important for us to engage in lobbying in the first place - to put forward the industry's views and put the record straight.'