Google are dishing out free Google Play Credit in the UK for Chromecast owners.
I've had both mine since a few days after they became available but according to the offers page that you go to through the Check Offers menu via the Chromecast app.
The free £20 is in addition to the Google Play Music offer, free movie rental and Sky Movies 2 month offer if of course you haven't already taken advantage of them.
Get checking now. The small print does say for Chromecasts purchased and set up between November 15th 2015 and 15 January 2016