When Theresa May took office in July, she declared an assault on inequality and an end to privilege in politics. Today she is flogging lunch with herself at her party conference for £3,150. We can assume the price does not reflect the food.

The prime minister may well be a hilarious conversationalist, but the business leaders and lobbyists who flood these conventions will be paying this money for advantage. Cash for access should not be part of Britain’s political culture. If parties need money, they should crowd-source it or raise it from members. They should not sell the public interest.

Hypocrisy has always been the least attractive of political characteristics. David Cameron’s crusades against corruption at home and abroad sat ill with his own susceptibility to lobbying – on everything from energy policy to airports to planning. His former strategy director, Steve Hilton, reported back from the recent round of American party conventions on “the revolting stench of corruption that permeated the proceedings”. One lobbyist told him that nowadays such conventions were “the bank”. Cameron’s Britain, Hilton implied, was going the same way.

Nothing seems to have changed. Almost Theresa May’s first decision was to capitulate to the sugar lobby over her anti-obesity strategy. The links between her aides and the lobbying industry are well-charted. Now she has given in to her party machine in conceding cash for access.

British politics may not be corrupt like Brazilian or Italian politics. Few British politicians grow rich, and ennoblement is a cheaper form of fund-raising than policy access. But the latter matters. Britain’s corruption is different. It lies in the networks and contacts, the winks, nods and patronage that infest Westminster and Whitehall. Above all, it lies in secrecy. This was bizarrely described by Cameron in opposition in 2010 as “the next big scandal waiting to happen”. He then let it happen.

The lobbyists’ professional association grew from five members in the 1990s to 80 today. At one point its revenues were rising by 20% a year. Businesses do not spend such money on lobbying for nothing. Every special adviser knows the industry offers a lucrative revolving door. Politicians will have friends, and their friends will have friends, some of whom buy lunch with the prime minister.

The only defence democracy has against such corruption is to expose it, and to ban such blatant instances of cash for access as £3,150-a-plate lunches with the prime minister. Meanwhile, might we at least see the list of acceptances?