Former treasurer Peter Costello co-owns Melbourne-based ECG Advisory Solutions with his one time political adviser David Gazard. ECG has Westpac, Transurban and detention centre operators Serco on its books.

Several lobbyists expressed surprise that Mr Costello and Mr Minchin are not listed on the official register of lobbyists. Ian Smith, owner of Bespoke, said Mr Minchin was a special adviser and was not directly lobbying the new government. ECG did not return calls.

One lobbyist, who did not wish to be named, said the nexus between business interests and power within the Liberal Party meant there would be greater potential for perceived conflicts of interest.

The biggest winner in the rush to conservative-aligned lobbyists is Barton Deakin, chaired by former NSW Liberal leader Peter Collins. Since the September election its client list has quadrupled to 63.

Barton Deakin is taking on eight out of 10 clients of the Labor-aligned Hawker Britton. Both companies are owned by STW Group and clients are migrated from one to the other depending on which side of politics is in the ascendancy.