A class intent on filling its boots with other people's money. Outrageous sums nodded through with barely a murmur of dissent from spineless committees. And suddenly-mutinous voters. No, not the MP expenses scandal, but another tale of egregious excess – this time in our corporate boardrooms.

The precise details of what Westminster's finest claimed on expenses may have variously shocked, angered and engrossed the country this month, but compared to what the directors of big companies get up with our politicians are, frankly, amateurs. Douglas Hogg may have taken a couple of grand to clean his moat, but Fred Goodwin convinced RBS to buy him an £18m jet – complete with personalised registration. Duck islands and pipes for tennis courts? Messrs Viggers and Letwin should really take a leaf out of John Thain's book. The former boss of US bank Merrill Lynch spent $35,000 of his company's money on a commode. Yes, you read that right: $35,000 for a toilet.

There is more to this roll call of excess than prurience. For a start, the all-expenses-paid lifestyle of the big corporate chiefs serves as an example to others both in other countries – ever the competitive sort, Mr Goodwin would have watched the packages awarded on Wall Street – in smaller companies and even in the public sector. How else would our parliamentarians have got the idea that £64,766 – a wage putting them comfortably in the top 5% of all single earners – was inadequate unless they had been comparing themselves to those raking in even more? This, presumably, is what the free-marketeers meant by the trickle-down effect.

Investors who are seeing their shares sink are finally asking why they should keep indulging the bosses of those companies. Last week, 59% of Shell's shareholders voted down its directors' pay packages – a huge rise from the 15 or 20% that might come out against a particularly obscene pay deal just a couple of years ago. And as we report today, there is disquiet among RBS shareholders over the deals offered to executives at the nationalised bank. Their complaints about big money tied to vague performance targets sound all too familiar.

But the big question is what took them so long? Shareholders may now be angry about the backscratching in the boardrooms of BP, Shell, Next and others – but none of this is new. And the real risk is that when the recession eases and markets head decisively north once more, the anger will dissipate and the culture of corporate complacency will settle once more, like so much displaced dust. This must not happen. Fat-cattery is fat-cattery whether it is in bust or boom. There are two problems that need to be resolved, one harder than the other.

The first and thornier issue is to do with investors. This is meant to be a shareholder democracy with ordinary Britons each holding a slither of our biggest businesses. Yet the pension funds which represent their interests are not bothered in scrutinising the companies, let alone having more of a say in running them, but only in trading their shares. Nor are they held meaningfully to account by pension-fund trustees. The second is the nature of company boards and non-executive directors in particular. Too often members of an old-boy network – "old" and "boy" being the operative words – who are sitting on several other boards at the same time, they are generalists rather than specialists and they tend to like a quiet life rather than standing up to self-indulgent management. This is an area of corporate life that has been examined time and again, ever since Adrian Cadbury's report in 1991. There have been improvements, but not enough. Our corporate boards must be made more diverse to rid them of the old stuffiness. A few workers' representatives among the non-executives would surely be more inclined to question outsize pay deals. The only way to reduce fat cats is by having more watchdogs.