Jane10 I suppose the best thing we can do is let it be known that we are not happy about the current situation. People sometimes deride those who sign on-line petitions but if it becomes clear that a large number of people are angry about a particular issue, it can yield results.
There are also various campaigns that need as much support as they can get - such as UK Uncut, which has massively raised the profile of the matter of tax avoidance/evasion, etc.
Also, if there is something local or national that you feel concerned about, write to your local MP. If enough people raise a particular issue, MPs start to sit up and pay attention.
It doesn't feel enough in the face of so much corruption and wrongdoing, but at least it's something.
It does seem extraordinary that in the facer of so much evidence about, for instance, child abuse within respected institutions, some people just won't accept that it has happened. I suppose if you have spent a lifetime believing that those in respected and powerful positions are beyond reproach, it is difficult to have everything you hold dear turned upside down. The danger of matters being "brushed under the carpet" (as they tried to do with MPs' expenses and child abuse) is that institutions as a whole lose credibility even though there are people within them who are decent and genuine.