The Ulster Unionist leader, Mr David Trimble, has said the SDLP "must start building their way toward supporting the police" in Northern Ireland because "they can't be in government" if they do not.
Mr Trimble has also hinted that the British government may be ready to allow the renamed Police Service of Northern Ireland to retain the Royal Ulster Constabulary's cap badge incorporating the Crown, Harp and Shamrock.
However, the deputy leader of the SDLP, Mr Seamus Mallon, has warned that he will not sacrifice his party's principles on the Patten policing reforms to help Mr Trimble overcome the renewed challenge to his leadership of the UUP.
He sparked fresh unionist fury by again insisting nationalists must "wait and see" the final shape of the Police (Northern Ireland) Bill before deciding whether they could recommend the new policing arrangements to the Catholic community.
Ulster Unionist Assembly Member Mr Fred Cobain said Mr Mallon was "seriously undermining his credibility within the unionist community". The North Belfast MLA said Mr Mallon's "wait and see" approach was "a disgrace, an insult to the police and not the kind of statement you would expect from a Deputy First Minister".
The First and Deputy First Ministers were speaking after separate talks in 10 Downing Street yesterday with the British Prime Minister, Mr Tony Blair.
Acknowledging Mr Trimble's difficulties, Mr Mallon told reporters: "I have tried to help them in every way I possibly can in terms of the working of the (Belfast) agreement and the working of the administration and will continue to do that."
However, he said, "I cannot sacrifice any of the fundamental factors of the agreement in relation to that problem or any other party political problem."
The Taoiseach, Mr Ahern, is understood to have reassured Mr Mallon and the Sinn Fein president, Mr Gerry Adams, that Dublin's position is unchanged on the key issue of flags and symbols for the new police service.
There is also no sign that either the SDLP or Sinn Fein would be willing to depart from the Patten Commission's central proposal that - as with title - the flags and emblems of the new service should be free of any association with the symbols of the British or Irish states.
Mr Trimble emerged from Downing Street to declare: "There are 66 other police constabularies in the United Kingdom. Every one of them has a badge with the crown on top. Northern Ireland is still part of the United Kingdom and that is explicitly recognised by nationalists in the agreement.
"The Secretary of State (Mr Peter Mandelson) has paved the way with regard to the badge for a more sensible conclusion. I think he actually needs to go further than that."
Later Mr Trimble told The Irish Times he expected the SDLP to embrace the new policing arrangements "because they can't be in government without supporting the police".