Durham Police has confirmed its backing for a "super force" to cover much of North East England.
Home Secretary Charles Clarke wants forces across the country to amalgamate to save cash and better use resources.
Northumbria Police has already given its support to a proposed merger with neighbouring Durham and Cleveland.
Now an internal study carried out by senior officers and staff from Durham Police has also backed the three-force merger plan.
Two panels, made up of senior operational officers and police staff managers, carried out an initial review of options drawn up in the wake Mr Clarke's September announcement.
They considered five options, including the merger with Northumbria and Cleveland and the creation of two city forces that would split Durham to cover the Tees Valley and Tyneside regions.
The result put the three-force amalgamation top, with the city force options at the bottom.
Durham's chief constable, Paul Garvin, said: "As far as the people of County Durham and Darlington are concerned, the case for a single regional force is, I believe, overwhelming and irresistible.
"We have had meetings with experts from all three forces and I have yet to hear any balanced or reasoned argument to change my mind."
Mr Garvin stressed that an in-depth cost-analysis of all the options, would be carried out by the end of November.
A final detailed assessment of the favoured proposal must be submitted to the government by 23 December.