I hate shopping at Christmas time. Aside from bargain rage you have to put up with Slade's Merry Xmas Everybody all day long. For people like me, price comparison websites can be a godsend, saving time, money and bother. But how effective are they?

Well I'm in the market for a new toaster. First I go to http://uk.shopsmart.com site, and look under home appliances. They have only one entry, and bizarrely it's for a Dyson DC05 vacuum cleaner. I switch to "electronics". But this time I get zero results. Hmm. Something's wrong here. No wonder Barclaycard is shutting this site at the end of the year. Time to try a different website. I go to www.priceguideuk.com, select "domestic appliances" type in "toaster" and immediately get 94 hits. Now that I have a list of products, I need to select one to compare prices against. I choose the Russell Hobbs 9376, Satin stainless steel toaster and get three results. The cheapest is from a company called Powerhouse, which is selling the toaster for £33.99, including delivery. I get the same price from www.kelkoo.co.uk, but from a different retailer, Comet. Taking a belts-and-braces approach, I search for the same toaster on the John Lewis website. It's cheaper, at £32.45, including delivery. OK, there's not much of a difference, but that figure could be a lot more significant on, say, a washing machine.

In spite of boasting a quarter of a million price comparisons, 250 retailers, and a daily price update, Priceguide.com is still not as comprehensive as it could be. Perhaps what we need is a meta-site to compare the price comparison websites.

These sites work by sending out shopping robots (bots) to scour the Internet for list prices. However, not all commercial sites allow bots access, so price comparison websites can't give the full picture. Also, beware of price-comparison websites that have affiliations with retailers and manufacturers. The cheapest product may not get the same prominence as the product from an affiliated company.

Most of these websites, such as http://uk.pricerunner.com, and www.onlinepriceguide.co.uk, as well as the ones mentioned above, compare prices on everything from beauty products to cars, but some specialise in one or two areas, such as utilities, phones, DVDs, or books.

For example, www.uswitch.com provides a simple facility to check whether you're getting a good deal on your gas and electricity. You just enter your postcode, the amount you pay on your utilities and hey presto, you're shown a list of suppliers that can provide the same service for less. For five second's effort, I learned I could save £141 per annum by switching suppliers.

There is also a range of sites for comparing the price of books. Bookbrain has a simple interface, but I found the 30-second response time excessive. Also, when I deliberately mis-typed the author's name I got zero hits, even though I'd included the title in the search. Bookcomparison is even worse. Search options are limited and inflexible - I looked for The Corrections by Jonathan Franzen and got 18 pages of results, including, Calvin & Hobbes Corrugated Flo. This is fuzzy matching gone wrong. 123pricecheck doesn't allow very sophisticated searches either, although the search is intelligent enough to offer Jonathan Franzen's The Corrections as one of its Top Matches.

My son wants the new Spiderman movie on DVD for Christmas, so I give www.dealtime.co.uk a spin. I click on Movies and enter Spiderman. Results: nil. Hey? The box-office hit of the year and no one's flogging it? I refine my search by entering Tobey Maguire under Actor/Actress. As the results trickle in, I realise my mistake - I should have spelled it Spider-Man.

I wonder if other websites are as unforgiving in the spelling department, so I give www.homeshopping.co.uk a go. It can't find any results for Spiderman, Spider-man or Tobey Maguire.

Last-chance hotel, I go to www.easyvalue.com and click on DVD. There's Spider-Man right at the top of the Top Ten Charts I don't have to type anything. I just click on the title and get the comparison list. The list is easy to sort, and you're provided with lead-times to delivery.

Price comparison websites are great if you're after big savings and don't care to see the look of gratitude in the eye of the salesperson as you fork out £5,000 for a plasma screen TV. Just make sure you've researched your product thoroughly beforehand and beware of the hidden extras. You might find that your bargain is suddenly out of stock when you refuse to buy the very expensive optional extras.

There isn't the space in this column to list all of the price comparison websites in the UK. For a full list, visit: www.uk.ciao.com/categories/1,14,15365,5017323.html.