It's been about a decade since the term "mortgage arbitrage" made headlines. It's back.

In the clearest sign yet of just how late far the investing cycle the developed world finds itself, the FT writes that wealthy British homeowners are again borrowing against their property to invest in bonds, equities, alternative investments or commercial property as the low cost of debt creates opportunities for “mortgage arbitrage”. And while taking out a mortgage to invest in "safer" arbs like corporate bonds, commercial real estate or private equity would be at least understandable, if not excusable, in the current low-yield regime, some more extreme "investment" decisions suggest that the madness and euphoria that marked the peak of the last asset bubble is back: because while growing numbers are prepared to risk using their primary residence as collateral, some are ready to gamble on extremely volatile assets like bitcoin, wine and cars.

One broker said a mortgage-free homeowner with a house valued at £10m had taken out a fixed-rate loan of just under £2m to buy bitcoin, the crypto currency that has seen huge volatility in recent months. Others have invested in classic cars or fine wine. One former banker took out a £500,000 mortgage, not for investment purposes, but to provide a fund for routine spending and other eventualities.

To be sure, while these are extreme - and for now rare - examples of investor euphoria, even the more mundane "mortgage arbitrageurs" are willing to take major gambles: "Interest rates of less than 2 per cent on two- and five-year fixed-rate home loans are tempting high-income, mortgage-free homeowners to raise money against their property in the hope they can profit from higher rates of return elsewhere."

Simon Gammon, director at mortgage broker Knight Frank Finance, said the arbitrage had emerged as a trend among financially sophisticated clients as mortgage rates fell. “We’re a specialist lender at the top end but we’re seeing up to a dozen of these deals a month,” he said. “This is something that has come about because of the current environment of low rates.”

How prevalent is this behavior which peaked during the last housing/credit bubble?

Mark Pattanshetti, a mortgage manager at broker Largemortgageloans.com, said the number of borrowers taking out loans to fund investments had risen by about 50% since 2009. “Borrowers have realised the cost of debt is cheap and it isn’t going to get much cheaper,” he said. Unfortunately, what borrowers are forgetting is that home prices can drop as mortgage rates rise, while risk assets - impossible as it may sound - can correct sharply, hitting borrowers with the double whammy of rising LTVs as inbound margin calls force them to liquidate into a sliding market.

Ironically, anecdotal evidence suggests that this troubling behavior has been prompted be declining UK home prices - until recently one of the best performing British assets. This has been the result of Brexit-related concerns, a decline in Chinese and other foreign investors rushing after UK real estate, as well as concerns that the BOE will soon raise rates, resulting in increasingly more "for sale" signs.

As the FT notes, "for debt-free homeowners, remortgaging during the years of booming house prices was often a means of raising cash to carry out home improvements or expand a buy-to-let portfolio. But slowing house price growth and a regulatory and tax crackdown on landlords have made these options less attractive.

Hugh Wade-Jones, group managing director of mortgage broker Enness, said: “It’s accepted that property is no longer going to be the all-conquering investment, doubling every 10 years, so people are looking elsewhere for returns.”

In addition to bitcoin, cars and wines, borrowers with housing equity are putting money into everything from bonds and private equity and commercial property, brokers told the FT. David Adams, managing director of John Taylor, a Mayfair-based estate agent, said investors were borrowing against London residential properties to fund investment in commercial and mixed use developments from Southampton to Birmingham at returns of 6 to 7 per cent.

“Wealthy investors are no longer chasing capital gain. There is a switch to yield,” Adams said.

According to Knight Frank's Gammon, the practice typically appealed to those with investment experience. “People who have not needed to borrow have looked at the rates available — and we’ve now got five-year fixed rates from 1.65 per cent — and said if I can’t make 1.65 per cent or more from my money, then I don’t know what I’m doing.”

Unfortunately, should home prices in the near future tumble while risk assets slide, crushing the "experienced" investors, that's exactly what one can conclude.

Making it easier for the "smart investors" to bury themselves with margin calls, there are no regulations prohibiting this kind of behavior:

There is nothing in mortgage regulation to prevent someone raising a loan on a mortgage-free property for personal investments, as long as the lender assesses that the loan is affordable and not being used, for instance, to prop up a business generating income for its repayment. Lenders, however, may choose to apply criteria that restrict the use of capital raised through a mortgage, although private banks are typically more relaxed about non-property investments than high street banks. For bigger mortgages, lenders will also moderate risk by insisting that the size of the loan does not exceed 60 per cent of the property’s value.

Naturally, it doesn't take a big drop in the value of the property coupled with a slide in the "alternative investment" to wipe out the LTV buffer, pushing the value of the loan above the underlying collateral. That said, "the Financial Conduct Authority, which regulates mortgage lenders, declined to comment on individuals borrowing against their house for personal investments."

In a tangent, the FT then focuses on the tax considerations of this risky behavior.

Unlike gains on a principal private residence, any gains on investments would be subject to capital gains tax (CGT). A wealthy homeowner may therefore seek to transfer borrowed funds to a spouse who has not used his or her annual CGT allowance. If the investment is designed to provide a stream of income, there could be a case for a transfer to a spouse who pays the basic rate of income tax, advisers said. Nimesh Shah, a tax adviser at accountants Blick Rothenberg, said that if a homeowner took out a loan to invest in commercial property — and this was specified as the purpose of the loan — residential mortgage interest could potentially be offset against the commercial rental income.

Of course, the above assumes capital appreciation and therefore, capital gains. For now nobody is worrying on the more unpleasant outcome, one where there are no gains to book taxes again. Then again, in a wholesale wipeout at least the "smart money" will have years and years of NOLs carryforward losses to offset any future income taxes. Just like Donald Trump.