Well, we all know that they lie, frequently, and swearing that they're telling us the truth while they do it. But what would be an example of 'the greater good'? We were lied to about WMDs in Iraq, as a justification to get the public onside to assist America to invade Iraq. So no example there - we knew the Govt. was lying, and our opinions and protests counted for nought. There is still a cover-up in place, thanks to the MoD, regarding the strange deaths at the Deepcut Barracks, and lies have been told to keep that beyond public knowledge. No example there - we know something's wrong when all of the evidence in each case was totally destroyed, but now we can't prove something's wrong.
There are lies told about British Nuclear Fuel's safety, about animal and human health, about terrorist activity, about pollution levels, about GM crops, MMR vaccines, and on and on. So what would be a JUSTIFICATION to lie about something else to the public, for the public's sake? We're so used to assuming that politicians LIE to us, that what could possibly be left for them to lie about? What would be so much more important than taking your country into combat, or covering up deaths, diseases, potential attacks upon your homeland, that it would be okay to lie (again) to the public - for the tattered remnants of their own 'good'?