The UK is poised to drop that crazy law that legally prevented people from using FM transmitters to send their iPod's buttery beats to their radio, so Britons will need to start shopping around for the myriad FM transmitters, the most promising of which is the iCast from iStuff. Given the official seal of approval from the UK's Ministry of Truth (or whomever), the iCast plugs right into the iPod's headphone jack, so it should work on other, non-iPod DAPs, too.
The iCast is capable of transmitting music between the frequencies of 88.1 MHz and 107.9MHz and is powered by a single AA battery (or you can plug her into the cigarette lighter).