Great, now I've got more Chromecasts than TV's. First world problems.

https://store.google.com/config/chromecast_2015

You have until 8am GMT :man:

Get 3 months of Netflix Service on Netflix’s “Standard” membership plan with each Chromecast activated between 6 December 2016 and 9 January 2017 (inclusive).

Netflix Standard membership plan is currently worth £7.49 per month if purchased separately on netflix.com(price correct as at 1 November 2016).

Offer only open to 18+ UK residents

Offer must be claimed via chromecast.com/offers or the Google Home App and the offer code activated on netflix.com on or before 9 January 2017.

The offer code is valid for 3 months of Netflix Service on the £7.49 (a month) Standard membership plan. You may apply the value of the offer to a different Netflix membership plan. Exchanges in this manner may alter the duration of the offer period. The offer is not redeemable or refundable for cash and cannot be exchanged for Netflix gift subscriptions. See http://help.netflix.com/legal/termsofuse

If you are an existing Netflix member (when claiming the offer), your subscription willautomatically renew on your current membership plan (Basic-£5.99, Standard-£7.49 or Premium-£8.99) at the end of the offer period unless you cancel your subscription. If you are a new Netflix member (when claiming the offier), your Netflix Service will end at the end of the offer period unless you choose to subscribe to Netflix. See Netflix.com for current pricing.

I collected my Chromecast from Argos this morning, the price had increased to £30 but as I had reserved it £20 thats the price I paid.
I signed up as a new Netflix customer and got 1 month free, then using the Google Home app offers received £22.47 of credit to my Netflix account (so in effect 4 months). Also got 2 months NOW TV Movies for £2 and 90 days free Google Music. Not bad for £20

Great, now I've got more Chromecasts than TV's. First world problems.

I bought one of the Tesco Chromecasts for £18 last week, and it actually came with a sticker on it promising three months of Netflix, not one! Haven't tried it though as it's a gift for Christmas.

You can also get this direct from Google for £20
(Audio is also £20)
https://store.google.com/product/chromecast_2015

Not recently, but then I'm not too interested at the moment anyway. I was more mentioning it in case it might actually be three months for the OP's Chromecasts.

any chromecast ultra offers?

Interestingly I just got an email from Argos about a Chromecast offer starting tomorrow (6th) where it says you get 3 months free Netflix, not sure if it is just a typo or whether they are putting on a new offer tomorrow. Will be interesting to see though the sceptic in me says if they are really doing 3 months the price will not remain £20 as the 3 months Netflix alone would be worth more....

Doesn't it just say "Start your 1 months free trial"? I would read that to mean that you get a month free when you start Netflix...

There isn't a link as such as it was just in the email from them, but I have put a screenshot below:
http://i236.photobucket.com/albums/ff137/stevenallickuk/test/argos%20promo%20email_zpsgnlzvgao.png

I went on chat to ask about it but the adviser didn't seem to know anything about it, though I suppose that is possible since it isn't actually live yet, assuming it isn't a typo, which wouldn't be a first for Argos....