Ex-NSW minister Chris Hartcher and his former staffer Tim Koelma spoke in code about companies that secretly funnelled nearly $400,000 to NSW Liberals, the corruption watchdog has heard.

The Independent Commission Against Corruption (ICAC) is investigating allegations Mr Koelma’s company EightByFive was a sham outfit, set up to allow banned political donors to secretly fund the 2011 election campaigns of NSW Liberal MPs.

Mr Koelma, it’s alleged, would then create phoney invoices so donors’ payments could be passed off as payments for media relations and strategic advice.

“Mr Hartcher was the mastermind of this. It was his idea to set up this business EightByFive which could then produce fake invoices and collect money on behalf of the Liberal Party,” counsel assisting Geoffrey Watson SC said on Wednesday.

“Absolutely not,” Mr Koelma replied from the witness box.

In a 2010 email obtained by ICAC, Mr Koelma updated Mr Hartcher on the status of his “Friends”: “Sydney – steady, meeting them next week. West – steady, discussing correspondence on Monday. North – nothing yet”.

He has told the inquiry these were his clients – property developer Gazcorp in Sydney, infrastructure firm Australian Water Holdings in the city’s west, and Nathan Tinkler’s Buildev up north in Newcastle – and he was keeping Mr Hartcher in the loop because he thought he would be interested.

But Mr Watson said Mr Koelma was updating his boss on money flowing in from the three companies and that a “code” was deployed to disguise contact between the parties.

“I don’t think it was a code, I think it was just a colloquialism,” Mr Koelma said.

Earlier on Wednesday Mr Watson repeatedly asked if Mr Koelma wanted to withdraw or retract any of his evidence so far.

“If you relent now and tell the truth people might go easy on you,” Mr Watson said.

“I’m not sure what you’re driving at,” Mr Koelma said.

“Well, at lunch you can take a cab out to Malabar and see exactly what I’m driving at,” Mr Watson retorted.

Malabar, in Sydney’s east, is home to Long Bay prison.

Anyone found to have deliberately misled the commission can be jailed for up to five years.