Boris Johnson's former top aide Eddie Lister was involved in discussions on a massive shake-up of planning laws despite being employed by two major property firms, it is claimed.
Industry insiders told the Mirror that the senior aide, who stepped down as No 10 came under pressure over conflicts of interest, had been advising on the proposals.
Whitehall sources also suggested that Lord Udny-Lister had been involved as the Downing Street policy team drew up the plans with Robert Jenrick's Ministry of Housing last year.
The peer has previously admitted he had "a couple of other bits and pieces" of work while he was in Government but argued there was no conflicts of interest and all had been declared.
Explaining why he had chosen to stand down from his most recent job as Gulf envoy, which he began in February, he said: "You can't be half in, half out of Government."
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© Fulham ChronicleEddie Lister
The radical planning reforms, now signed off by the Prime Minister, will be one of the Government's flagship policies in next week's Queens Speech.
The new law will overhaul rules that slow down and obstruct house-building and force all councils in England to dedicate land for either development or preservation.
One development industry insider said: "Eddie was involved in the evolution of planning policy that was announced in Jenrick's white paper.
"It was a wholly untenable position in light of the conflicts of interest."
Lord Udny-Lister was an adviser to property group Delancey and a non-executive director to Stanhope Holdings during his time at No 10.
The Tory peer admitted he had attended several meetings where the planning changes had been discussed - but denied he was a key architect of the plans.
He told the Mirror: "I was in various meetings where the subject came up. I was never part of the detailed work on this.
"It was mainly done by the No 10 policy team and MHCLG. My hands are well away from this one."
But shadow Communities Secretary Steve Reed said: "The Conservatives are giving developers more control over planning and gagging communities so local people lose the right to object.
"We need to know urgently what role Lord Lister played given the conflicts of interest now coming to light in his relationships with wealthy developers who donate increasing vast sums of money to the Conservative Party."
Labour's Rachel Reeves has written to Cabinet Secretary Simon Case to ask him to look into any potential conflict between Lord Lister's public and private roles.