While Mr Morrison has previously not responded directly to questions about his position on the matter, the Prime Minister wrote to Mr Barr late last month ruling it out.

The ACT's police force is contracted out from the Australian Federal Police, meaning federal parliament would need to change the ACT's self-government act to allow the territory's integrity commission to investigate allegations of corruption or serious misconduct in ACT Policing.

Mr Barr wrote to then-Prime Minister Malcolm Turnbull requesting the changes last year, before raising it with Mr Morrison in August last year, after his elevation to the job, with the Prime Minister formally responding in late February.

The territory's police have been pushing against the move for almost three years, citing existing oversight mechanisms at the Commonwealth level, such as the Australian Commission for Law Enforcement Integrity, despite calls for a national commission, given weaknesses in the existing oversight mechanisms.

Mr Morrison wrote that having received advice from Attorney-General Christian Porter and Home Affairs Minister Peter Dutton on the matter, the government did not support the territory government's proposal.

"Any delineation between ACT Policing and the broader AFP would be legally and practically problematic," the letter reads.

But Mr Morrison, echoing former ACT chief police officer Justine Saunder's offer, also wrote the federal government was open to "exploring ways to strengthen information sharing with the ACT Integrity Commission to enhance the level of insight into ACT Policing integrity matters".

While Mr Morrison earlier this year announced the Coalition would pursue a federal anti-corruption commission, the government's proposal has been criticised by several experts, including former NSW ICAC Commissioner David Ipp QC, who said it created a wall behind which public officials could hide.

The territory government also sought changes to federal telecommunications interception and surveillance laws to allow the integrity commission to fully use its proposed powers to investigate allegations of corruption and serious misconduct.

Mr Morrison wrote the Home Affairs department would work with the ACT government on those changes, noting that due to the sequencing of legislative amendments, there may be a period with the ACT commission did not have access to those powers.

Mr Barr said police should be covered and it was disappointing the current federal government was standing in the way of extra integrity measures.

But he said the issue would be revisited after the impending federal election, should there be a change in government.

Mr Morrison's office did not respond to requests for comment about the issue on Monday.