By Martin Lewis Published: 10:25PM GMT 29 Nov 2009  And whether it's lack of political will or clout, nowt is being done to stop it.  Subtract Bank Rate and lenders are effectively charging four percentage points more than a year ago, adding about £300 a month to homebuyers' costs per £100,000 of mortgage. While many don't perceive a rate rise – after all, 5pc mortgages still sound pretty cheap – put it in the context of the bigger picture.  To say British interest rates are low right now is a bit like saying expenses caused MPs a small PR issue. Interest rates aren't just low, they're limboing 1.5 percentage points beneath the recorded 200-year historic low.  The Bank of England reason for slashing rates was to stimulate the economy, yet lenders' puckish response is clogging our nation's financial arteries. While, as I'll explain later, you can improve things for yourself, it's approaching time for action from Westminster.  The evidence - must admit a wee glee of nerdish frisson here, as it's time to play with the stats.  Stark reading! While Bank Rate plunged by 4.5 percentage points, this mortgage rate's barely wobbled, dropping just half a point.  So while the margin over Bank Rate was 0.5 of a percentage point, it's now a staggering 4.5 percentage points. Or phrasing the numbers more viciously, mortgages were 10pc higher than the Bank Rate; now they're 900pc higher and fees are higher now, too.  Yet I'm being slightly disingenuous; I suspect any mortgage brokers reading this will be yelling that fixed rates don't actually follow Bank Rate.  Their funding's more closely associated with swap rates, which, in simple terms, are the City's current view on interest rates over a set period.  For variety, let's switch to two-year fixes; a year ago they were 6.3pc while two-year swap rates stood at 5.3pc, a decent but probably fairish profit margin. Now the gaps become a yawning gulf; fixes are 5.1pc while swaps are at 2.1pc.  Part of the reason for margins this wide is the huge drop in the volume of mortgages, a classic lack of demand – due to more stringent criteria and the slowing remortgage market. Yet it's still a massive hidden rate rise.  Of course, there are some winners – the few with pre-Bank Rate nosedive trackers are probably still gleefully boogieing around their homes. However, new mortgage hunters can't snoop out such glory rates. Trackers now average three percentage points above base rates, where once it was half a point.  Perhaps the biggest scandal, though, isn't special-offer discount or trackers; it's the standard variable rates you automatically flick to when these end.  Once the default ''flee from'' option as they were extortionately expensive, it's not just those in negative equity who now have nowhere cheaper to go. The spectre of what I call evaporating equity is hitting many.  This affliction means you can't get a new mortgage deal due to a double-whammy…  Pre-credit crunch, loan-to-value (LTV) ratios of more than 100pc were possible (borrowing more than your home's value) and competitive rates were available at 95pc LTV. Now to get a decent deal, you need to borrow less than 75pc of your home's worth and this cuts huge swathes of existing mortgage holders out.  The ''value'' bit of LTVs means current house price values, so where prices have fallen, people's LTVs have worsened. Many once in that competitive sub-75pc zone aren't anymore.  Yet even with so many on these standard rates, look what's happened to them. The average gap over Bank Rates used to be about two percentage points, and when rates were first slashed, government pressure to keep it there was partially successful, yet now the gap's a mammoth four percentage points.  The paradox is that while mortgage rates have been relatively unresponsive to falling Bank Rate, it's likely they'll be overstimulated when they rise.  Millions are locked into standard rates or high-margin trackers, or due to be when their current deal ends. When rates do finally turn and start to rise, it'll be like a smash-and-grab brick through windows.  Imagine Bank Rate returned to last year's historically still quite low 5pc, someone with a £200,000 interest-only mortgage tracker today would see their payment explode from £500 to £1,330 a month.  • Bagsie a cheap fix for insurance. Many with deals ending ask if it's worth fixing now to future-proof against rate rises, even at a higher cost than their standard variable rate. A halfway house is using the little-known option of paying a fee to book a current fix to start between three and six months ahead. Then if rates or future fix prices rise, you can use this, if not, simply don't use it and lose the fee.  • Repay your mortgage with savings. You're less at mercy from mortgage rate rises, and it helps lower your LTV, possibly meaning access to more competitive deals. The mathematics to decide if it's worth it are simple (assuming there are no overpayment penalties). If your after-tax savings rate is lower than your mortgage rate, pay it off.  • If you have other more expensive debts, pay those off first. Keep an emergency fund – as with most mortgages, overpayments can't be borrowed back. For more and a special calculator, see my full guide at www.moneysavingexpert.com/repaymortgage  • Build a war chest. If you're on a super-cheap rate now and haven't got savings, put money aside.  • Get a mortgage broker. Have a broker on call to speedily grab short-lived deals, preferably one who's ''whole-of-market'', meaning he or she must look at all the mortgages available to it. Find out more at www.moneysavingexpert.com/mortgagebrokers  • Should you ditch your fix? For most, exit penalties added to high new mortgage rates mean you're unlikely to save any cash – plus you lose the fix's security. If you want to do the numbers, a calculator will work out whether it's potentially worth it for you at www.moneysavingexpert.com/ditchfix  Martin Lewis, Money Saving Expert, is a specialised broadcaster and more than 4m people get his weekly money tips email at www.moneysavingexpert.com/tips
Mortgages across the country are being overpriced &ndash; a ticking time bomb    ready to blight the finances of millions.