The reason you cannot get "Radio 4 UK Only" outside the UK is not a technical issue, its a legal one.
Because the BBC in the UK is funded by the licence payer, it is not allowed to be broadcast outside the UK by the BBC, a third party can re-broadcast it as happens for example on satellite.
The same happens if you go to the BBC web site, in the UK I can listen and watch programmes which have been previously broadcast on TV & Radio, but from outside the UK most of them you cannot receive, this is also a copyright issue.