IN ACCORDANCE with the ever reliable mote-and-beam principle, it is almost always unwise to tell other people how to spend their money.

But, by suggesting that rich people should give more of their "colossal wealth" to charity, the Mayor of London, Boris Johnson, recently offered welcome advice at a time when the gap between the lifestyles of those on the rich list and those (many more) reliant on unemployment benefit and food banks is widening at a worrying rate.

Against the background of what the Office of National Statistics has estimated as a ten-per-cent rise in house prices in London over the past year, our indigenous and imported millionaires are reportedly finding it difficult to buy a house in that always tricky £30-50 million bracket. As a result, everyone from internet entrepreneurs to hedge-fund managers is finding it a struggle to get on the super-prime property ladder.

Their hardship, however, compares with that of the tens of thousands of council tenants who face eviction after falling into rent arrears after the introduction of the so-called "bedroom tax" earlier this year. Those tenants might wonder how many rooms are left "under-occupied" in a multi-million-pound pile crammed with home cinemas, en-suites galore, and basement swim­ming pools. But such reflection will get them no­­­where - as well they know. 

So Mr Johnson's intervention is not only timely, but far likelier to get people thinking honestly about such massive inequalities. Not,
of course, that inequality per se is always to be derided. After all, you can have equality and equality of opportunity - but not both. Or, to put it another way, there will always be someone with a bigger house than yours.

And yet there is clearly something not quite right about a system that allows a number of individuals to satisfy their self-indulgence in ways which princes and potentates of old could only have dreamt of, while others are forced to choose between heating their modest homes, or eating.

As the Mayor suggested, the trend in the capital and elsewhere is now to kit out a home with every mod con imaginable, and to live in total isolation from the daily realities of life as experienced by the majority of our fellow citizens. 

An equitable taxation system aside, compul­sion is arguably not the way to iron out these growing disparities. You may wish that the über-rich would rein in their expectations, but forcing them to do so would generate unwelcome con­sequences further down the line.

In a roster of names stretching from Benjamin Franklin to Bill Gates, the United States has a long tradition of civic philanthropy that, the Mayor says, British moneybags have been un­­willing to embrace for fear of seeming ostenta­tious. "Absolutely ridiculous," the Mayor says; they should give more to charitable causes rather than satisfying "their lust for buying great schlosses in the Home Counties".

As he predicted, he was setting himself up for criticism from all quarters: from those who give generously (but anonymously) already; from those who see private philanthropy as an excuse for government to shed its responsibilities; and, indeed, from those who helpfully pointed out that Mr Johnson's own house (or one of them) is itself valued at £2.3 million.

But, as a general prod in the backs of the rich and privileged, his suggestion had an honest and heartfelt ring. Whether those of us with a mite more in the bank than we need will heed his advice is another story.

Trevor Barnes reports for the Sunday programme and other BBC Religion and Ethics broadcasts.