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You might think you're displaying savvy shopping techniques by sticking to supermarket own brands, but if you reach for the items without checking prices, the chances are that you've seen the cost of some items in your trolley rise by up to 50%.
So what's going on?
A report by The Grocer, has found that the prices of supermarket own brands are going through the roof.
It said that some supermarkets have increased the price of more than 40% of their own brand range. At Tesco, over 43% had gone up in price (although 28% had fallen in price). At Sainsbury's 41% had risen in price, and 37% had fallen in price. Only Asda had lowered more prices than they had increased.
Tesco and Sainsbury's told The Grocer that they were doing everything possible to keep costs down, but in some instances they had needed to put up some prices because of the rising costs of production.
Elinor Zuke, a journalist with The Grocer, told AOL: "Commodity price inflation is the problem. You can't get around the fact that animal feed is getting more expensive, and the cost of distribution is rising."
This matches the research from the British Retail Consortium, which found that food price rises have been accelerating towards the end of the year.
Stephen Robertson, British Retail Consortium Director General, said: "Costs for commodities such as wheat and corn have eased off since peaking earlier in the year but these pressures, coupled with the impact of poor harvests, are continuing to filter through to fresh foods, with meat, fish and vegetables hit particularly hard."
The Department for Environment, Food and Rural Affairs says that this is just the latest piece of bad news in a long line, as food prices have risen 12% in real terms over the last five years - taking us back to 1997 in terms of cost of food relative to other goods.
And the trend is unlikely to change any time soon. The Grocer concluded that the cost of the weekly shop was likely to rise at least 4% a year for the next decade at least. Zuke said: "A lot of it is dependent on the weather, but we will at least have to wait until next year when the current crop is harvested before there's a hope of prices coming down, and even then we don't know that they will because we don't know what that harvest will be like"
Of course, this doesn't mean we ought to shun own brands, as costs have risen across the board. Zuke says savvy shoppers are increasingly buying own brands, which now appear in 80% of all Tesco trolleys and 72% of those at Sainsbury's. She adds that all the supermarkets are increasing their range of 'lower budget ' food by an average of 20% - which shows we are pulling out all the stops to cut costs.
However, these findings serve as a useful reminder that any shopping-by-habit can be risky. It's worth taking the time every-so-often to check the alternatives, to ensure that the products that were the cheapest last time remain so now.
10 of the biggest consumer rip-offs
Supermarket own brands shock price rise
Using a mobile phone to make and receive calls, send texts and browse the web while abroad can be extremely costly – especially if you are travelling outside the European Union (EU), where calls can cost up to 10 times as much as at home.
To avoid high charges, Carphone Warehouse suggests tourists ensure a data cap is in place, use applications to check data usage, turn off 'data roaming', avoid data-intensive applications such as Google Maps and YouTube and use wi-fi spots to update social networking sites.
Payment Protection Insurance (PPI) is supposed to help people to continue meeting their loan, mortgage or credit card repayments if they fall ill or lose their jobs. However, policies are often over-priced, riddled with exclusions and sold to people who could not make a claim if they needed to.
At one point, sale of this cover - which was often included automatically in loan repayments - was estimated to boost the banks' profits by up to £5 billion a year.
Now, though, consumers who were mis-sold PPI can fight back by complaining to the bank or lender concerned and taking their case to the Financial Ombudsman Service (08000 234567) should the response prove unsatisfactory.
It could be you, but let's face it, it probably won't be. In fact, buying a ticket for the Lotto only gives you a 1 in 13.9 million chance of winning the jackpot.
With odds like that, you would almost certainly be better off hanging on to your cash and saving it in a high-interest account.
No-frills airlines such as EasyJet may promote rock-bottom prices on their websites. But the overall fare you pay can be surprisingly high once extras such as luggage and credit card payment fees have been added - a process known as drip pricing.
Taking one piece of hold baggage on a return EasyJet flight, for example, adds close to £20 to the cost of your flight, while paying by credit card increases the price by a further £10.
It may therefore be worth comparing the total cost with that of a flight with a standard airline such as British Airways.
Cash advances, which include cash withdrawals, are generally charged at a much higher rate of interest than standard purchases.
While the average credit card interest rate is around 17%, a typical cash withdrawal of £500, for example, is charged at more than 26%.
What's more, as the interest accrues from the date of the transaction, rather than the next payment date, costs will mount up even if you clear your balance in full with your next payment.
Supermarkets such as Tesco and Asda often run promotions under which you can, for example, get three products for the price of two.
However, it is only worth taking advantage of these deals if you will actually use the products. Otherwise, you are simply buying for the sake of it, which is a waste of your hard-earned cash.
Buy a train ticket at the station on the day of travel and the price is likely to give you a shock - especially if you are travelling a long distance at a busy time of day.
However, you can cut the cost of train travel by 50% or more by going online and making the purchase beforehand - especially if you book 12 weeks in advance, which is when the cheapest tickets are on sale.
Other ways to reduce the price you pay include avoiding peak times and taking advantage of so-called carnet tickets, which allow you to buy, for example, 12 journeys for the price of 10.
Most High Street banks offer packaged accounts that come with monthly fees ranging from £6.50 up to as much as £40, with a typical account charging about £15 per month.
Various benefits, such as travel insurance and mobile phone insurance, are offered in return for this fee. But whether or not it is worth paying for them depends on your individual circumstances.