More than half (51 percent) of online retailers are spamming web user with emails that they have not requested to receive, says Spam Ratings. According to the spam research firm's first 'Spam Report', more than two in five (44 percent) of firms automatically 'opt-in' customers for marketing emails, rather than letting them decide if they want to receive the emails.

This means the firms are ignoring advice from the Information Commissioner's Office  which states the onus is on companies to ensure that proactive consent has been obtained before emails are sent and a pre-ticked opt-in box for consent to send email marketing should not appear.

Furthemore, 56 percent of emails sent from the UK's top 100 brands were not asked for by consumers. PC World, B&Q and the Arcadia Group are among the firms guilty of this.

In fact, Spam Ratings, said the Arcadia Group as one of the worst offenders for sending unasked for emails. If a web user signed up to the Arcadia Group's major high street names: Topshop, Dorothy Perkins, Miss Selfridge, Top Man, Wallis, Evans and Burton, over six month they would have received 394 emails that were not explicitly asked for - that's more than two emails per day.

The spam research firm revealed that 13 major brands, including Boots and British Airways, contradict best practice guidelines by automatically 'opting-in' customers when it comes to receiving emails from third parties.

Just one in three UK brands both meet email marketing best practice standards and don't send emails that customers have not explicitly asked for.

"Trusted brands are making a big mistake by not acting responsibly, openly and fairly with customers. Businesses spend millions building brands and then seem intent on destroying them by sending millions of useless, unwanted emails," asaid Andy Yates, co-founder of Spam Ratings.

"Big brands need to start acting responsibly now. Give consumers a fair choice. Let them choose if they want to receive emails. Common sense tells us that if consumers actively request emails then they are more likely to read them than delete them. Responsible brands need to communicate and have a dialogue with consumers rather than annoy them."

Following the publication of the report, Asda - one of the firms guilty of sending out spam emails – has revealed it is currently reviewing its email marketing policy. "Asda is happy to work with Spam Ratings as it reviews its email policy as part of its ongoing commitment to provide great customer service," the supermarket said.