In addition to owning lots of stations, GWR try to get away with producing as little content as they're allowed to and sharing it across those stations.
There are rules set out by The Radio Authority about how many national and regional stations there can be, how many hours of locally-produced content each station must have, and so on.
GWR is a critic of this, and has recently accused The Radio Authority of being dictator-like. It's akin to Microsoft complaining that the Department of Justice are stifling their innovation.
They do, however, get away with as little local content as they can, through networking. Their FM chain of stations is known as The Mix network, which largely have the same format and playlist consisting of chart, pop and dance acts, and the slogan "Today's Best Mix" (until recently "Today's Better Music Mix)
These stations each have their own local Morning Crew show, and their own local programming during the mornings (such as 'workplace of the day', where the Black Thunder jeeps pay a visit and let the staff have a bit of a party on air).
At night, pretty much everything is networked. The Hot 30 with Mel and Rob is on from 7 till 10 during the week, with dedications from around the country (although some stations have the same format with different presenters), and Late Night Love is on from 10 till 1, Sunday to Thursday. There's also the Friday Night Party Zone, their commercial dance show. Almost all of the stations broadcast The Pepsi Chart on a Sunday afternoon.
GWR Group run a digital station (on Sky Digital channel 920) called The Mix, This is largely automated, but does have occasional presenters, and seems to be keen on requests. Network shows like the Hot 30 and LNL, and overnight shows are carried on this channel too.
One thing which is common to almost all the stations is a playlist. It's not uncommon for all the stations to be playing the same songs in the same order at the same time, and links between songs won't deviate from what's on the screen in front of the presenter - where the only difference is the DJ's voice.
The target audience for this network is females aged 24 to 35.
GWR also own a handful of AM stations, some of which are part of the Classic Gold network. Not all of these are owned by GWR - some are owned by holding companies which GWR owns enough of a stake of to in order to control the output.
Other digital radio stations they run are Core and Planet Rock, in addition to the national FM franchise, Classic FM, and they own the 63% of the franchise for the national digital radio multiplex, Digital One.
Most of this information was gleaned from spending too much time at media uk, www.mediauk.com. Please /msg me with corrections and omissions