Many lottery spam scams in particular use UK 070 prefix telephone numbers as a means of contact. These look like mobile numbers, but I've known for a while that they are actually "personal numbers" which the owner can redirect to anywhere. Thus, if you move around a lot, you can forward the number to new locations as you go.
What I didn't know was that you could obtain one of these numbers without being in the UK, and forward it to a number which is also outside the UK. Consequently, all those lottery scams which appear to be UK-based thanks to UK phone numbers aren't necessarily in the UK at all! Furthermore, the sign-up process can be done online, just like signing up for a free webmail address, so the scammers aren't even obliged to re-use the same number on their next scam. All in all, UK 070 numbers (starting with "+44 7" when expressed as an international number) tell us absolutely nothing about the location and identity of the party so contacted.
Thanks to Sophos for pointing this out.