Since I joined up to giffgaff, I followed the advice to set up iPhone and installed the giffgaff profile.
As I have an unlocked Italian iphone, I often SIM-swap and find that the profile kinda takes over everything and is a bit of a hassle to adjust (though for some reason the APN giffgaff.com does not inhibit use of a 3IRL and 3UK SIM).
Today, this caused me no end of problems while trying to configure a brand-new 3 Italia iPad microSIM and, in order to get the latter to work, I had to remove the giffgaff profile. Once done, data flowed.
Now, having dispensed with that, I put the giffgaff back in for home use and instead of re-installing the giffgaff profile, I simply adjusted the APN from the default O2 one to the giffgaff one. It worked.