I don't know when this will stop working, what I know is that it is currently working (it has been tested and confirmed by over 30 people)
-Playstation Network account (make a dummy one from UK)
-A Credit Card(They will charge you after your 14 days of trial, just cancel it the last day and they won't charge you)[
1-Go to PlayStation®Plus - Claim your 30 day free trial
(Facebook and IGN no longer offer 30 days codes.)
2-Claim your code, you should receive them in a few hours.
It works more than once but to do it I recommend you using different IPs (Hide my IP for example or hidemyass.com) and e-mails.
To activate your codes, follow this tutorial :Redeem a voucher code*-*PlayStation Support Guides
The codes will only work on a UK PSN account. If you don't have one already, register here:PlayStation Registration and then retry entering the PS store with that new account .
To not get charged, cancel the PS+ subscription 1-2 days before it expires. Because if you don't they will charge you and extend your PlayStation Plus subscription . Thanks for understanding.
If you have any question,quote me and I will get to you as soon as possible, thanks