What is the uk law regarding police informants?

A police informant has made a false allegations against me.The police are bending over backwards to suppress his background and criminal history.I am told that even if this went to a jury they could hide this fact from the jurors but the judge could be told about the informant by letter but would also not disclose any details about the informant and would sit back and see a misccarriage of justice!I Is this correct and what are the safeguards against informants providing false evidence?