The British government is finally
considering legalising low-power FM transmitters, of the sort used to transmit sound from MP3 players to FM radios. In the UK, anything that transmits on licensed frequencies (such as those used for FM radio), at any power level whatsoever, requires a licence from the Secretary of State; (In contrast, in the US, it is legal to use transmitters below a certain power level without a licence.) With the popularity of iPods and their ilk, the law hasn't been enforced as rigorously as it might be; the devices started appearing quite openly in shops on Tottenham Court Road a year or two ago, with the retailers, when questioned, hemming and hawing about the legality of using them.
Any change in the law to legalise the devices will require them to "meet strict technical standard to minimize interference to other radio users". Presumably these will include making them robustly unmodifiable to prevent them from being adapted into high-power FM transmitters, which are in demand by the large numbers of pirate radio stations across the UK.