Amazon Prime ads sent in the post failed to adequately inform people that a £79-a-year subscription for the service would automatically kick in following a 30-day free trial.

The ban has been enforced after the UK's advertising watchdog, the Advertising Standards Authority (ASA), received six complaints about the ads. The complainants had two main gripes. The first was that the ad did not make it sufficiently clear that a paid subscription would automatically start if not cancelled during the free trial; and secondly it did not state what the cost of the subscription would be.

Amazon said that the ad campaign in question was not currently being distributed but argued that in the "Offer Terms" section in small print at the bottom of the letter, the company explicitly stated that:

Paid subscription starts automatically after the free trial unless cancelled

However the ASA said that it considered a paid subscription starting automatically at the end of the trial to be a commitment and a significant condition of the "free" offer, and should therefore be made clear to consumers.

"The text in the main body of the ad stressed the 'free' nature of the offer and noted it did not refer to the automatic paid subscription."

Likely to mislead

Relating to the absence of a reference to the cost of the £79 Prime subscription, Amazon said that it would be plainly obvious when users when to register for the free trial on Amazon's website.

The ASA didn't accept this argument however: "We did not consider it was sufficient to set out that information in the subsequent online registration process. Therefore, because the subscription fee was not detailed in the ad, we concluded that the ad was likely to mislead."

The ASA said the ad must not appear again in its current form and it has told Amazon to "ensure that the significant condition that the paid subscription started automatically after the free trial unless cancelled was included in the main body of the ad and that the ad also informed consumers of the extent of the financial commitment they must make if they did not cancel the subscription during the trial".

Corporate rape

The controversy around Amazon Prime's dubious sign-up practices were brought to the fore in February when restaurant critic Giles Coren found he had been paying for the service without his knowledge for three years.

Coren rather crudely called the tactics employed by Amazon as "cynical corporate rape" and compared the commerce giant to a "sicko porn site" in a tirade on Twitter.

Amazon for its part says that people who find they have mistakenly signed up for Amazon Prime but haven't used any of the services it offers (free next-day delivery and access to Amazon Instant Prime Video service) can apply for a complete refund.