I open this thread to keep track of solutions for the small carriers like Giffgaff, Virgin Mobile, etc. who don't offer nano sims for the iphone 5.
For giffgaff there's this thread stating that they won't have nano sims for months (people seem to be rushing out of gg and asking for PAC codes): http://community.giffgaff.com/t5/Blog/giffgaff-nano-SIM-update/ba-p/5953002
For Virgin Mobile for the sound of it there won't be nano sims in the near future, there are no news from the official channels: http://community.virginmedia.com/t5/Mobile/Nano-Sim-on-Virgin-mobile/td-p/1451072
For giffgaff there's this thread stating that they won't have nano sims for months (people seem to be rushing out of gg and asking for PAC codes): http://community.giffgaff.com/t5/Blog/giffgaff-nano-SIM-update/ba-p/5953002
For Virgin Mobile for the sound of it there won't be nano sims in the near future, there are no news from the official channels: http://community.virginmedia.com/t5/Mobile/Nano-Sim-on-Virgin-mobile/td-p/1451072