Northern Ireland Secretary Dr John Reid tonight urged all sides in the province to stop playing politics with the new policing board.
As Mr David Trimble insisted he choose one of his Ulster Unionists as the first chairman, Dr Reid demanded attempts to influence him must stop.
He warned: "I will not be lobbied by politicians or interested parties on any side of the political divide."
With speculation intensifying over who will head the new body overseeing RUC reform, Mr Trimble insisted independent representatives' claims should be ignored by choosing a politician to head the 19-strong board.
"I think the natural appointments would be a UUP chair and an SDLP deputy chair," he said.
The board is made up of 10 politicians and nine independents.
Sinn Fein's refusal to take its allocated two seats because republicans claim police reform has not gone far enough, means Ulster Unionists have four representatives while the Democratic Unionists and nationalist SDLP each have three members.
In a letter to Dr Reid, Mr Trimble argued he would be guilty of returning to the "bad habits" of direct rule by ignoring political representatives' claims.
Mr Trimble voiced concerns that the SDLP were lobbying Dr Reid to come down in favour of a nationalist chair.
The UUP chief insisted he had a statutory duty to ensure not only the board, but its chair and vice chair, are representative of the community as a whole.
"It therefore means that other things being equal, the Chair should be occupied by someone from a unionist background and the deputy chair by someone from a nationalist background."
But Dr Reid hit back, saying: "If people insist on playing politics with positions on the new policing board its task of bringing about the new beginning to policing which the people of Northern Ireland want will become ever more difficult."
He said a selection process for those members of the board who wish to be considered for the roles of chairman and vice-chairman was ongoing.
A Northern Ireland Office source expected the four-strong panel to meet in the coming days.
The SDLP refused to respond to Mr Trimble's demands that the UUP should head up the board.
The Ulster Unionist leader's call came as he arrived in London tonight for a series of briefings with journalists on his bid to remove republican ministers from the Stormont Executive because of the IRA's failure to disarm.
A delegation of UUP MPs and MLAs will also travel to Dublin tomorrow to meet Irish political parties to emphasise unionist demands that the Provisionals must now put their weapons beyond use.
PA