I have found a way to give yourself literally Unlimited Free credit on Blinkbox!!
1) Just head over to http://www.blinkbox.com/register/metrofive
Register your details to claim your £5....
when blinkbox send you an email to with a 4digit code on.... IGNORE this email!
2) Click on the little blinkbox logo in the top left hand corner, then click logout
2) Register your details AGAIN using the same link.... http://www.blinkbox.com/register/metrofive
3) just repeat and repeat the step's to get as much credit as you like. at the moment i have £125 in my account. each time you register you get ANOTHER £5.