Deputy PM Dominic Raab has paid his own legal fees during an investigation into allegations he bullied officials.
's spokesman said it was "not an option" for his legal representation to be paid by the government.
This is despite taxpayers footing the bill for Boris Johnson
's lawyers in the Partygate inquiry, which so far runs to £220,000.
Downing Street is facing questions about why Mr Johnson
is getting government support.
Rishi Sunak's spokesman said the former prime minister was being investigated over government business when he was a minister.
He argued that this was different to Mr Raab
's case and meant that Mr Johnson
was entitled to government support under an "established process".
The PM's spokesman denied both men were being investigated over their behaviour and were therefore subject to the same rules.
- whose legal team is headed by top barrister Lord Pannick KC - is facing claims he deliberately lied to Parliament over Covid
-rule breaking in Downing Street when he was prime minister.
The Commons Privileges Committee is currently deciding whether he is guilty of a contempt of Parliament. Mr Johnson
was last month grilled for nearly four hours by the committee, with a lawyer at his side.
is under investigation over eight formal complaints about his behaviour as foreign secretary, Brexit secretary and during his first stint as justice secretary.
He has denied allegations of bullying and said he has always "behaved professionally" - but has previously said he would resign if the inquiry finds against him.
The bullying probe is being carried out by lawyer Adam Tolley KC, who was appointed by Mr Sunak in November.
Mr Tolley's report is expected to land on the prime minister's desk shortly. He will then decide - based on the evidence in it - whether Mr Raab
has broken the ministerial code and must be sacked.
News that Mr Raab
had paid for his own legal advice was included in a much-delayed update to the register of ministerial interests, published by the government in the wake of controversy over Mr Sunak's financial transparency.
's entry in the register reads: "The minister has engaged lawyers at his own expense in relation to the investigation being conducted by Adam Tolley KC."
Ministers are meant to register shareholdings, directorships, investments or any other financial arrangement that could lead to a conflict of interest.
It is unusual for a minister to declare an expense on the register, as Mr Raab
A Cabinet Office source said ministers can also use the register to declare "anything that is relevant to their work as a minister".