Anyway, can you confirm at least that my initial contention, that it is not possible to call a normal UK number and get billed for an international/premium call, is correct?
Yes you only get billed whatever number you dialled at whatever rate your tariff dictates.
I reckon Milo jumped to conclusions too quickly and there is potentially more to the story than meets the eye because it sounds like a very tall tale at the moment (sounds a lot like one of those chain mail emails that go around that have no resemblance on reality .... you know, the
"IF ANYONE CALLS AND ASKS YOU TO DIAL XYZ THEN DON'T WHATEVER YOU DO OTHERWISE THEY GET FREE INTERNATIONAL CALLS FOREVER AND THIS HAS BEEN CHECKED BY THE POLICE AND EVERYTHING IT'S COMPLETELY TRUE SO DON'T DO IT. P.S. DON'T FORGET TO FORWARD THIS TO EVERYONE YOU KNOW." sort of thing).