By CNBC's Robert Frank.

The wealthy often buy their most prized possessions at auction: art, jewelry, wine and even mansions.

Now they might be able to bid on an even bigger auction prize: visas. U.K. entry visa.

In the latest twist to the global drama over luring rich emigres from China, Russia and other countries, an immigration official in the U.K. is proposing a plan to auction off visas to the overseas rich, with minimum bids starting at $4 million.

The program would be a first of its kind in the world. And the U.K.'s Migration Advisory Committee report said that any surplus from the bidding could go to good causes like assisting inner-city schools or health-care research.

Skeptics, however, say such a plan would create "eBay immigration" for the rich, where a country simply sells access to the highest bidder—regardless of their longer-term value to the country.

"It sends the wrong message to the public," Sophie Barrett-Brown, a U.K. immigration lawyer told The Times of London.

But the policy only makes official what many countries are already doing.

As the world's rich—especially from China and Russia—look to safeguard their families and their fortunes, many are fleeing to other countries.

And governments hoping to attract the overseas rich have created special fast-tracks for big investors.

In Australia, 91 percent of the 545 applicants for the country's "significant investor" visa program are from mainland China.

The program only requires a $5 million investment and clean criminal record.

Chinese luxury spending fell 15 percent last year, the biggest decline in five years.

CNBC's Robert Frank reports on the falling sales of Chinese luxury goods and the migration of the super wealthy.

But some governments are starting to ask tougher questions about the benefits.

Canada this month decided to kill its controversial investor visa program after it was inundated with tens of thousands of wealthy Chinese applicants.

Under its plan, people worth a minimum of $1.4 million could get a visa if they loaned the government $720,000 interest-free for five years.

The Canadian Department of Finance said the program "significantly undervalued Canadian permanent residence."

(Read more: Chanel 'tours' tailored for Chinese big spenders)

The U.S. EB-5 program, known as the investor visa, is also coming under fire for providing far fewer jobs and economic benefits than promised.

The Brookings Institution this month released a report saying that the program—which gives a visa to those investing $500,000 or more or creating or preserving at least 10 jobs—needs more oversight.

"There is a dearth of reliable and publicly available data that would enable better monitoring and evaluation of the economic impacts of regional center investments," Brookings said.

And next to Britain's $4 million, American visas still look cheap.