Ofcom is legalising the use of FM transmitters that allow iPods and other MP3 players to play through car radios.
The devices allow iPods to be used in cars
The use of devices, such as Griffin's "iTrip", was banned in the UK as their transmissions can interfere with broadcasts by legal radio stations.
However, the device and other similar accessories for MP3 players have been widely available online.
Now certain FM transmitters, which can be tuned to spare frequencies, will be legal from 8 December.
Ofcom will also remove the need for a licence to use Citizens' Band radio.
The regulator's move follows a public consultation exercise.
Stamp of approval
The devices fell foul of the Wireless Telegraphy Act of 1949, which forbids the use of radio equipment without a licence or an exemption.
But strong consumer demand for the devices led Ofcom to rethink the legislation.
Liberal Democrat MPs were also prominent in asking for iTrips and similar devices to be legalised.
The new Wireless Telegraphy (Exemption) (Amendment) Regulations 2006 mean that certain low-power transmitters will now be legal.
However, many devices currently on the market will remain illegal as they do not meet the legally required technical specifications and could interfere with radio broadcasts.
The new amendments will also reflect a European standard on the low-power transmitters.
All approved transmitters will carry a CE mark indicating approval for sale in the European Union.