Marks & Spencer's website has topped a new ranking of user-friendly websites, with its fashion retailing rivals Next and Top Shop struggling at the bottom.
Online shopping records are set to be broken again this Christmas
Web usability consultants Webcredible assessed the websites of 20 of the UK's most popular High Street retailers.
It cited confusing search results, poor navigation and complicated checkout procedures as the worst mistakes.
E-tailing trade body IMRG has estimated that shoppers will spend £7bn online this Christmas, 40% up on 2005.
A number of High Street stores have announced plans to ramp up their online offerings ahead of the key Christmas trading season.
Webcredible measured the online stores against 20 usability criteria including navigation, product display, the checkout process and search capability.
It then ranked them in order of user-friendliness, putting Marks & Spencer top with a score of 81% and Clinton Cards bottom with a score of 25%.
Other stores tested included Currys, Debenhams, Woolworths, WH Smith, Boots and the Early Learning Centre.
"Independent research shows that as many as 83% of internet users leave a website because they can't find what they are looking for," said Trenton Moss, director at Webcredible.
"Our study threw up some real surprises - Top Shop doesn't even provide a search function and, incredibly, the Clinton Cards website gives users the option to add products to their basket without actually letting them know how much they cost."
Kim Gilmour from Which Computing magazine said that shoppers are looking for online stores that are uncluttered, well-signposted and quick to load.
"People want to find the item they're after quickly and complete the checkout process with minimal fuss."
No one wants to spend precious time laboriously trying to find their way around an unintuitive, badly-designed site - they'll quickly take their business elsewhere."