Lyrically, the song is an attack on the music policy of what was (at the time) London's only legal commercial music radio station, which played mainstream chart hits and little if any punk. It mentions the station's then-Head of Music, Aidan Day - "He picks all the hits they play/to keep you in your place all day".
They're even worse because they had the chance, coming right into the heart of London and sitting in that tower right on top of everything. But they've completely blown it. I'd like to throttle Aiden Day. He thinks he's the self appointed Minister of Public Enlightenment. We've just written a new song called Capital Radio and a line in it goes "listen to the tunes of the Dr Goebbels Show". They say "Capital Radio in tune with London". Yeah, yeah, yeah! They're in tune with Hampstead. They're not in tune with us at all. I hate them. What they could have done compared to what they have done is abhorrent. They could have made it so good that everywhere you went you took your transistor radio — you know, how it used to be when I was at school. I'd have one in my pocket all the time or by my ear'ole flicking it between stations. If you didn’t like one record you'd flick to another station and then back again. It was amazing. They could have made the whole capital buzz. Instead Capital Radio has just turned their back on the whole youth of the city.
The song ends with a parody of one of Capital's actual jingles of the period; the band replaces the lyric "in tune with London" with "in tune with nothing". The parody is heightened by the use of a variation on the ending riff from 'I'm only dreaming' by the Small Faces.
Stiff Little Fingers use a modified version of the chorus as the outro to their song "You Can't Say Crap on the Radio".
The extended play Capital Radio was released on 9 April 1977, and was given away to readers who sent off the coupon printed in the NME, plus the red sticker found on the band's debut studio album The Clash (1977). It was produced by Mickey Foote and engineered by Simon Humphrey. The interview was with the NME's Tony Parsons.
In 1978-79, "Capital Radio One" was extremely rare in the UK, so much so that the group had re-recorded it as "Capital Radio Two" on the extended play The Cost of Living, which was released on 7-inch vinyl on 11 May 1979 through CBS Records. "Capital Radio" was re-recorded because the group learnt that copies of the original Capital Radio EP were selling for high prices. "Capital Radio Two" is longer (3:19), mainly because of a protracted intro and outro. "Capital Radio Two" has been included on Super Black Market Clash (1994) and Singles Box (2006).