Ray Boulger at Charcol, the broker, expects it to reach 1.5% by the end of 2010, and George Buckley at Deutsche Bank is pencilling in a rise to 2%. However, Savills and Mortgage Force, another broker, believe it will rise more rapidly, to 4% by the end of next year.

Borrowers also need to factor in how long Bank rate will stay at 0.5% before starting to rise. Separate research from L&C shows Bank rate would have to stay on hold until April 2012 before you would be better off with a tracker.

On a £200,000 repayment mortgage, you would make repayments over the five years of £75,594 on a fix. The tracker would cost less at £75,190 if Bank rate stayed on hold until April 2012 (then rose at the same speed at which it fell). If Bank rate started to rise in February 2010, as many expect, the tracker would be £13,000 more expensive than the fix over the term at £88,848.

“If you’re a homebuyer, or on an expensive variable rate, it’s worth fixing now,” said Melanie Bien at Savills.

You need a 40% deposit with the Post Office deal. NatWest has a five-year fix at 4.89% for those with a 25% deposit.

The decision is harder for those on ultra-low tracker rates, some of which are lifetime deals. Someone on a tracker at 0.5 percentage points above Bank rate — so 1% — now pays £167 a month on a £200,000 interest-only loan. If you fixed at 4.5% you would pay £750 a month — £583 more.

Bank rate would have to rise to 4% before repayments on the tracker would exceed those for the fix. If it hit 4% at the end of 2010, you would have saved £10,494 in the intervening

18 months by sticking with the tracker, but this assumes rates stay at 0.5% for the whole period — an unlikely scenario.

ENERGY

About 4.6m households are on fixed or capped tariffs, and Scottish Power and Npower fixes expire at the end of July.

A typical fixed deal taken out in July last year, just before a series of price increases, cost £1,045 a year. Today, the average standard plan costs £100 more at £1,145, according to Uswitch, a comparison firm.

Last week, Consumer Focus, a consumer watchdog, hit out at energy firms for failing to pass on price cuts. Wholesale rates are down 53% since their 2008 peak, while domestic energy prices are down just 5%.

Uswitch said consumers might be better holding off to see if rates fall further. Opting for an online deal and paying by direct debit could shave £200 off standard rates, it said.

However, those who want the security of a fix should act fast. Joe Malinowski at theenergyshop.com said: “Fixed-price deals take account of anticipated future wholesale price rises — and the pressure is upwards if you take into account the price of oil. Even if prices are cut on standard deals, fixed price deals may not come down at all.”