Income and wealth however are completely different. There is often a good correlation but not always.
Compare a 50 year old "normal" worker, has paid off his mortgage and owns outright his £250k house (he bought it cheap 25 years ago). He earns £25k a year. Pays a low amount of tax on his £25k income, and a very low % if you consider his wealth (ie £250k asset of his house)
The other guy is a superstar recently graduate banker, has just started earning £200k a year in the city. Hes paying off his student loan, and also a lot of tax on his "high" income. Hes got no wealth, hes renting a flat and spending the vast majority of what he takes home right now as hes been used to living on nothing and is living the hig life. His % tax to assets is absurd.
Our current system basically is the above, for individuals the vast majority of tax take is based on income not assets (or wealth). If your assets do not generate income then they are just about tax free, say your house goes up in value by £25k in a year (like happened to a lot a few years back) your wealth has gone up, but you have paid no tax. Theoretically you could have sold the house and pocketed £25k (lets ignore the somewhere to live element).
Over a medium term period you do get typically a very good correlation between income and wealth but it takes time, not only for people to convert income into wealth, but also for some assets to increase in value (property/land etc).
But wealth is taxable. Capital Gains Tax being the most obvious one on the sale of appreciated wealth (as per your house example). Stamp duty is also tax on the accumulation of wealth (of which property likely makes up the largest portion of wealth in the UK, given that home ownership is around 90%). For all other forms of wealth, there is Inheritance Tax which is levied upon the total value of your estate at death, provided it is over a certain threshold.
Sure, you don't pay for your wealth whilst it is wealth, but as soon as you want to turn it into something that you can actually spend you're clobbered by the grey-suited ledger-wielders at HMRC.
For me the biggest and most fundamental issue is do we want a rebalancing to take place on income vs wealth as a general population. Associated issues then spring up, high wealth is not a guarantee of ability to pay. If your only asset was a £500k family home which you own outright but a retired and just scraping by on your pension and the system suddenly changed to make you owe £10k tax per year due to your wealth how would they pay it? Would it be fair they may have already paid loads in income tax.
The simplest way to collect tax is on earnings, by the very fact you have just earn't it, deducting a chunk at source means you must have the ability to pay it.
If you did move to a wealth based system then lets assume you have to fill in a form, list all property, shares, savings, vehicles(?), company shares or value of own sole trader(?), then those assets could be assessed for tax. How would you police it, how would you value the items without a quick simple market price? Lots of work = significant people to do the work (tax men)
This is an interesting point. Although not commonplace elsewhere, if you are caught committing certain crimes (speeding is the one that springs to mind) you can be asked for a statement of wealth by the court. This requires you to detail your personal wealth, including properties and business interests, so that you may be fined according to your wealth rather than your income.
Obviously, this is a rather exclusive way of taxing wealth as you need to commit a criminal offence, but the wherewithal to do it is already in place. I'm sure this method also comes into use when calculating retroactive taxes due, a possible example being the closure of certain tax loopholes.
What about when markets crash, everyones wealth declines = less tax, or possibly no tax depending if you tax wealth increase or wealth as an absolute.
The same issue with wealth will happen as with income tax, the richest are those most likely to be able to afford to manipulate the tax by structuring to avoid. Eg if its a personal wealth tax then setup a company to own your mansion and pay a peanuts rent. When completing the form you own no property wealth to be taxed. Company wouldnt earn any profits so this is where you would have to again be taxed on shares owned or you could simply avoid the wealth tax this way.
Not strictly true, certain types of wealth depreciate in a market crash, others appreciate. Precious metals and commodities are the prime example of wealth that appreciates when markets crash, whilst property usually depreciates as liquidity dries up. For everybody in a crash who loses, there are those who have won. Excluding the 2008 scenario, this has been true of every market crash.
As a broader point, I think it's important to remember that income tax rates are seldom paid at their stated rate. Depending on an individuals circumstances, their income may suggest 20% income tax but due to something like a company car their marginal rate of tax is higher as their personal allowance is reduced. Generally speaking, the higher your income and wealth, your affairs become all the more complicated and you can start facing marginal tax rates of over 60%.
It appears to me that due to the insane complexity of the UK tax code, politicians have carte blanche to bang on about how people should pay more tax without actually having a working understanding of the tax system. Rather than having the endearing qualities of a child, Clegg's ignorance is an affront to anybody who actually bothers to sit down and work out what they're paying each year to HMRC.