Calls with CLI's beginning 04
I find it interesting seeing just how many calls I'm getting from numbers beginning with 04 and other number ranges (specifically within the 03 range) that Ofcom haven't released.
Ofcom coould quite easily require all operators to block any call that uses a UK CLI for a number that hasn't been officially released by and registered with Ofcom.
Likewise they could make the operators do similar for other holes in the international number ranges.