Sales of DVD box sets have surged in recent years and the phenomenon looks set to continue as the TV industry identifies them as a lucrative new income stream and a way to allow consumers view their favourite programmes at a time that suits them.

"The advent of the DVD has revolutionised TV viewing, " Jennaro Castaldo of HMV told the Sunday Tribune. "Collections never worked on VHS as videos used to take up too much room but DVD sets have a lot of appeal. The popularity of US dramas and comedies has given rise to their popularity. Friends probably started the trend and then programmes like 24, The Sopranos, and Sex in the City were developed and became popular on DVD."

Castaldo believes TV has become diluted with the number of digital channels available and that this had led to people missing their favourite programme. "The West Wing used to be on Channel Four and then, after two series in, it was transferred onto E4. After this change, I found that I had lost my way with the change-over and I found that it was harder to follow the series.

"A DVD gives you the freedom to watch a programme at your leisure. This is better as a programme such as 24 is entirely based on it being watched sequentially. With the box set, you can watch a whole series over a weekend."

Professor Helena Sheehan of the School of Communications at Dublin City University believes that the hours people now spend commuting between home and work curbs the amount of time they have for watching television. "A lot of people say they prefer the experience of watching TV series in box sets, because it is a more concentrated and coherent experience than watching series strung out over weeks, " she said.

Another academic, Dr Edward Brennan of the School of Media at Dublin Institute of Technology, maintains that box sets have sprung from a need for the industry to diversify its income streams. As a result of the increasing numbers of TV channels, the advertising market has become more fragmented so the TV spot ad is no longer viable as a means of supporting the industry.

"Box sets are also a cultural artefact that many people want to have and display in their homes, " said Brennan. "For some people, collections like The Blue Planet and The Sopranos may be regarded in the same way that people saw literature in previous generations."

Meanwhile, Dermot Horan, RTE's director of broadcast and acquisitions, said, "The shows that sell are high-quality shows that take a lot of involvement from the viewer.

People have busy lifestyles and they could be watching a series for the first few episodes and then go away on business to find themselves missing a few episodes and losing out. With shows like 24, Prison Break and Lost, people lose track when they miss an episode so box sets are a fantastic way of catching up."

Horan pointed out that shows with 'intrinsic quality" such as The West Wing never rated well on either RTE or Channel Four, but have sold very well as box sets. "HBO shows all sell well in box-set format as the viewer often benefits from repeatedly watching them. With a show like The Sopranos, the viewer sees things in the second viewing that they might not see when they first watch it."