Giffgaff? Lyca? Else? They seem to have the same tariffs but Lyca says it is preactivated which sounds pretty interesting given the fact that you can't be sure you can successfully activate a Giffgaff number from overseas(?). Giffgaff's site is
pretty clear regarding prices, Lyca's is quite annoying: you have to select countries one by one.
As I understand the minimum top-up is GBP 5 (for all carriers), but as Lyca is preactivated I may use it even with zero balance for incoming calls whenever i'm in the UK. When outside the UK, I just want it to produce the "this number is not available at the moment" sign, but not the "this number is not activated yet" sign, preferably without having to top it up with GBP 5 from abroad, which may or may not work anyways. As I understand, I can keep alive a UK number by sending a text to that number every 6 months?