Quote: I would ask our ex-patriot friends to do the same so the Revenue do not know where the call is coming from
But that is the whole point, donquixote.
If caller ID works across international boundaries (and that is a complex, vexed and inconsistent issue), then the called party will effectively see that the call is from overseas by the caller ID. If not, then it will appear as 'private number' - or some such other non-identification code.
For example, if I get a call from the UK (to the US),
when caller ID works, I will see 447984xxxxxx or from Australia 6189232xxxx. The first numbers immediately tell me it is from the UK (+44) or from Australia (+61).
The Tax Office would see the same, I guess - 1930555xxxx from the US, for example.
We have no need to try and "fool" the system. It is designed for us! (And I doubt if we could, anyway)
The saving grace is the fact that it is
NOT consistent, so 'Private caller' could be an overseas caller or an internal UK caller who has dialled 141 as a prefix. They have no way of knowing and so must answer the call.
Keep the b******ds guessing, I say.....!