Interactive TV software vendor OpenTV has marched into a long running patent battle between Amazon.com and Barnes and Noble over one-click shopping, claiming that it was the first to patent the technology.

Amazon has always claimed that it patented the concept and is asserting its rights as patent holder against arch rival Barnes and Noble.

However, OpenTV, a France-based provider of software for 10 million installed digital TV set-top boxes, said it recently applied to extend one of its own patents to include one-click shopping.

Amazon has licensed its '1-click' technology to other major ecommerce websites, such as Apple's online store.

Craig Opperman, chief intellectual property officer at OpenTV, said: "In our view, one-click shopping is very useful to interactive television. We believe the US Patent (5819034) clearly describes single interaction shopping in client/server and interactive television environments."

"Amazon could be precluded from using its patent against anyone practising what is taught in our patent," he added.

US patents don't, however, carry the same weight as they do in the UK. Many thousands of patents are issued every year in the areas of 'Computer Systems' and 'Computer Applications'. To qualify for registration, an invention is supposed to be 'new' or 'not obvious'.

The main problem is that the US Patent Office is overrun with applications and doesn't have the resources to research 'Prior Art' to the level of detail required. Prior Art is the term used for evidence that proves that the idea isn't new.

Indeed, this has resulted in a number of everyday interactions being patented. For example, using a credit card to buy goods online, and electronic shopping carts (OpenMarket 5715314 and 5724424), embedding hot links in emails to past customers, and saying 'click here for our new site' (NetDelivery 5790793) and rewarding people for reading your advertising (Cybergold 5794210).

Even hyperlinks - without which the web wouldn't exist - were called into question this summer when BT claimed that it owned the patent.