Ian Macdonald's former chief of staff, Tony Hewson, has admitted he has worked as a professional lobbyist for several years despite having never signed on to the official NSW register of lobbyists.

Mr Hewson has told the Independent Commission Against Corruption that he "didn't feel it was necessary" to register after he left Mr Macdonald's office in 2007 and picked up several resources companies as clients.

Those clients included White Energy and Felix Resources, two companies associated with the same company directors that ran Cascade Coal, which in 2009 was awarded a lucrative coal exploration at Mt Penny, near Mudgee, by Mr Macdonald's department.

That tenement sat underneath three properties controlled by the family of Labor powerbroker Eddie Obeid, and the family also took a secret 25 per cent stake in Cascade. This coal tender is at the heart of the present inquiry, after the ICAC alleged a "criminal conspiracy" between Mr Obeid and Mr Macdonald.

Mr Hewson accepted he had enjoyed extensive access to Mr Macdonald on behalf of his clients, including being able to sometimes enter his office without appointment.

The Commission heard that Mr Hewson's company, Dissolve Barriers, received almost $750,000 from White Energy and Felix Resources between October 2007 and February 2011.

Mr Hewson admitted lobbying Mr Macdonald to re-open a government tender to include White Energy. However, a private company Cascade Coal, which contained five of White's directors, was awarded the Mount Penny exploration licence in the re-opened tender.

In March 2011, during the final days of the NSW Labor government, then planning minister Tony Kelly oversaw the transfer of 70 hectares of Crown land in the Hunter Valley to White Energy for only $1.

Mr Hewson, who said he was employed as a government relations adviser by White Energy, admitted lobbying his former boss Mr Macdonald as well as Mr Kelly, for the $1 land sale to White Energy.

In early 2011 White Energy, a publicly-listed company, offered to buy Cascade Coal for $500 million. Five White Energy directors, John Atkinson, John McGuigan, Brian Flannery, Travers Duncan and John Kinghorn, were also investors in Cascade Coal.

The sale did not proceed after White Energy's independent directors begain asking questions about the Obeids' involvement in Cascade Coal.

The inquiry has heard that in order to "sanitise" the Cascade Coal sale to White Energy the Obeids extracted a $60 million payout.

Mr Macdonald will give evidence this afternoon.