Hmm, I've got a problem with this. Let's first of all start with a whopping assumption. Let's assume that salary is the only method of remuneration for top earners. There can be no share options, dividend payouts etc...
Now, if you cap the level of reward for top earners as being (for example) 50 times the annual salary of the lowest paid in the company, you end up creating a flat rate for our top bods which will be 50 x the minimum wage.
Minimum wage is currently £6.08 so (assuming a 40 hour week, 52 week year) such a proposal would cap top directors pay at £632,320. Fair enough you might think. It would certainly be a comfortable living standard.
There are a couple of downsides though. Firstly, any large organisation which employs people on minimum wage would be allowed to pay their directors no more that £632,320. The head honcho of successful companies which are booming (I'm thinking of the boss of Tesco?s here) will now be capped at the same rate as the guy in charge of a failing company (think Woolworths).
There would be no opportunity for a failing company to recruit a better, more experienced CEO. There would be a brain drain to companies in territories not covered by this law. There would also be a shortfall in the amounts of Income Tax raised, leading to tax rises elsewhere in the economy.
There is, however, an alternative, a simple and democratic solution to this problem that requires no laws to be passed and no parliament time. Go out and buy a couple of shares in whatever company gives you the hump. Make a point of turning up at the shareholders AGM and make your feelings heard. If enough people agree with you the company will have to reduce the pay of its top earners.