Differences between the UK and the USA
Geographical closeness of cities in the UK mean that the amount of choice, in terms of sheer number of radio stations, is limited on analogue when compared with the US. (The UK has approximately four hundred radio stations; the US has over 13,000).
However, obligations placed on Ofcom and its predecessors of ‘increasing listener choice’ have resulted in less duplication of format.
Formats are mostly music-based, with generally one mainly-talk channel available in each major city, provided by the BBC. Unlike the US, there are few commercial talk providers: the national talkSPORT (which covers more than just sports news), London's two LBC channels, and Edinburgh's allTALK are the only commercial speech stations.
Commercial radio
In the US, commercial radio carries two standard length of ads: 30 seconds and 60 seconds. However, in the UK, commercials vary in length from 10 seconds to 60 seconds or over, in multiples of ten seconds. Prices are based on thirty second commercials, and a percentage is applied for commercials of other lengths. A typical radio station media pack (http://www.virginradio.co.uk/sales/mediapack/index.html) shows the relative pricing: a 60 second commercial is not twice the cost of a thirty second, for example.
Commercial radio does not syndicate shows in the same way as, for example, Russ Limbaugh's show in the US (or the myriad of NPR stations). Some radio groups do some off-peak syndication, but the majority of programming is live or voice-tracked for the station itself. With very few exceptions, notably the top 40 chart on a Sunday, radio groups never share syndicated programming with others.
Frequencies
Europe uses different AM frequencies - there are no stereo broadcasts on AM, so stations are 9kHz apart, instead of the US’s 10.
The US only uses odd-numbered decimal channels on FM - that is for instance 98.3, 98,5, 98.7, and not 98.4 and 98.6.
Digital radio
The Ibiquity ‘HD Radio’ standard is not used within the UK, and digital broadcasting occurs on separate frequencies in Band III using the Eureka 147 standard (known as DAB Digital Radio).
A satellite service similar to XM/Sirius does not currently exist in Europe.