The Prime Minister re-enforced the message in his Commons speech, praising the RUC and promising that nothing would be done to undermine its security role.
"In respect of the RUC, I pay tribute to all they have done and will ensure that no changes will inhibit the proper fight they have against terrorism and crime of all sorts," he said.
Mr Mandelson, Secretary of State for Northern Ireland, confirmed a Bill to reform the RUC is to be introduced as part of the programme for the coming session of Parliament.
The details will not be announced until a consultation period on the Patten report, which finishes at the end of November. Mr Mandelson rejected suggestions in a letter to a cross-party group of MPs that reform of the RUC should take place only if there is decommissioning of IRA weapons.
The most controversial proposals include a change of name and removal of the crown from the badge to gain more acceptance for the Northern Ireland police in the Nationalist community.
Accepting much of the Patten report in its entirety, Mr Mandelson said: "I am also conscious of the specific concerns you have highlighted about changes to the name and symbols of the RUC and the dangers of premature implementation of some security sensitive measures."