"I also strongly believe that pay at the top of private firms/banks is out of control and will cause social tension and unrest in the end."
But what exactly can be done about it?
The only real option is, as you say, to get the Shareholders of the Company to do something.
But the problem is that if the management at Company A are not being paid as much as the management at other companies then they will up sticks and move.
Or if the Government tries to do something and impose a wage ceiling then you risk whole companies moving to countries where such things don't exist.
And that latter one is a particular risk for the UK. We've allowed ourselves to become utterly dependant on the financial sector when it comes to both jobs and giving money to the Government through various taxes.
That financial sector is really pretty mercenary and doesn't really have any physical ties to a location. Those aspects were what enabled us to lure them to London and Docklands in the first place.
Those same issues will also enable them to move overseas if the going gets tough here. Other countries will offer them the tax breaks and pay freedom that they want and they'll go.
We'll then loose the last major industry left in the UK and then the Public Sector will really be in trouble as tax revenues collapse. And that's also why the banks were allowed to get away with behaving as they did, we've become dependant on them.
"Morals" and fighting an "unequal society" are all well and good but when your society depends on business more than that business depends on you and there are other countries who are more than keen to accept those businesses then you need to be careful.