The locks restrict the transfer of songs or films between devices

If a compatible system cannot be created, an alternative method must be adopted, the National Association of Recording Merchandisers (Narm) added.

There are currently several different technologies which limit how CDs, DVDs and downloads can be transferred.

Record and film companies argue digital locks help to prevent illegal copying.

Files without copy protection, they argue, can be freely shared or traded over peer-to-peer networks.

However, there has been criticism from consumer groups such as the UK's National Consumer Council.

If consumers are discouraged by compatibility constraints and conflicts, we fear they will be less inclined to purchase more music and other digital entertainment content National Association of Recording Merchandisers

Restrictions on the way music tracks or movies are switched from one device to another are "constraining the legitimate consumer use of digital content", the council claimed in January.

Narm called for a "meaningful dialogue" between retailers and the entertainment and technology industries to find "reasonable solutions that will ultimately benefit everyone involved, most importantly consumers".

Its statement went on: "If consumers are discouraged by compatibility constraints and conflicts, we fear they will be less inclined to purchase more music and other digital entertainment content, and may instead choose illegal options."

The legal digital marketplace would be "derailed" without an end to the "confusion, frustration and disillusion" caused by having several digital rights management - or DRM - systems, it warned.