Personally I’d be cautious about using the latest quarter’s YOY growth figure of 19% to predict future growth.

My reading of historical data for the last few years is that digital radio growth has being following a fairly linear path. In other words, the percentage growth has fallen slightly each year as a comparable number of new listeners (and hours) is added as in the previous year.

- Digital radio’s share of listening has typically gone up by an average of about 3 percentage points per annum (this trend is more or less apparent for about the last 5 years, although it depends slightly on which quarters you compare).
- Annual DAB set sales (which drive the majority of the increase in digital listening hours) have shown pretty much no growth since 2007, having stuck at about 2.0 – 2.2m p.a. in each of the last three years. In other words, new opportunities for digital radio listening are being added to the market, but the rate at which this occurs is not accelerating.

There is some evidence that 2010 may be different. Firstly, there are grounds to expect DAB set sales to receive a one-off boost in Q2 2010 – perhaps of 50% or more – due to the Radio Amnesty promotion. Secondly, digital’s share of listening made a big jump in Q1 2010. Whether this is part of a trend, or just a blip (like the fall in digital’s share recorded in the previous quarter), may not be clear for several more quarters.

It’s hard to make an accurate forecast with so little forward visibility, but my more cautious reading is that switchover will be delayed by more than just a year or two. In other words, the digital radio growth curve will continue to look rather more linear than exponential.

Ed Vaizey, the culture minister, will acknowledge listeners’ frustration as he commits the Government to “support the ambition” of turning off the FM radio signal in 2015.