Borrowers are learning once again a hoary old truth about financial products. Unlike the famous slogan for wood varnish, they very often don't do exactly what it says on the tin.

Thus tracker mortgages, despite the name, do not always track base rate. As millions of tracker mortgage borrowers have already discovered, lenders are invoking special clauses to avoid having to pass on interest rate cuts once base rate sinks below a certain point.

With base rate already at its lowest level since the Second World War, and very probably sinking even lower in the next couple of months, these special clauses, known as collars, are being invoked with increasing frequency.

So long as these adverse terms were spelt out clearly to the borrower when the mortgage was sold, this is perfectly fair. One of the reasons lenders could price tracker mortgages as cheaply as they did was because of this hedge. Borrowers on tracker mortgages that were devised and sold before the credit crunch began 18 months ago are already paying very low interest rates. Even with collars, they are still being charged as much as two or three percentage points less than borrowers with fixed or traditional variable rate loans.

However, lenders very often did not alert customers to these collars. Some banks perhaps genuinely believed that they would never be triggered. But others buried the clauses in the fine print. Halifax was recently pressured by the Financial Services Authority to honour the spirit of its tracker mortgages after failing to include the information in its key facts documents sent to every customer.

Consumers - and increasingly ministers and regulators - are showing less and less tolerance for the weaselly ways in which the financial services industry too often sells its wares. From “precipice bonds” to split capital investment trusts, from credit card repayment terms to payment protection insurance, the industry has an unhappy record of devising products with terrible flaws or of jaw-droppingly poor value.

With three of the biggest players now in business only because of the taxpayer, that tolerance will be in even shorter supply.