It can be a little confusing knowing where you can buy a giffgaff top-up voucher. So hopefully this may help.
You can go into the following stores and ask for a giffgaff voucher:
So look for these signs:
If you need to know where these outlet are, please use the following sites:
If you cannot find one of these outlets, then you can go to a supermarket and ask for an O2 voucher.
nice and clear, its funny....i never really noticed these signs before but since joining giffgaff i see them all over the place.....just shows you, your eyes only see what they need to (or the mind rather).
It has been established that you can also use Tesco Mobile vouchers too.
It was posted on here by a couple of people that Tesco vouchers would work, but then a few more people tried them and they didn't work - including me.
I think that people had bought an O2 voucher from Tesco and got the wrong idea.