The Chromecast Audio (item no. 497/9144) is currently retailing at £24+ elsewhere and Google is recommending a £30.00 RRP. It's not the £15.00 deal from the Black Friday/Cyber Monday period, but my time-machine's broken :(
Quidco's offering 3.3% cashback on smart technology.
Khush01 found it on Google Store at £20.00 if you prefer purchasing through them: http://www.hotukdeals.com/deals/chromecast-audio-10-off-was-30-now-20-google-store-2566965
Hope this helps!