Bill,
The main service fuse is located on the board right next to the meter. This board is mounted inside the house in all older installations, or in a meter cabinet outside for some new homes.
Although accessible to everyone, the fuse carrier is sealed by the power co., as is the meter case and terminal cover (meters here aren't the plug-in type).
The short leads between fuse block & meter are clearly visible to the meter reader, so any tampering here would be spotted fairly easily.
I think the most vulnerable area is the cable before the fuse in homes with an overhead service. The overhead lines terminate on a bracket at roof level, then two double-insulated single cables run from there down to the service block.
In some homes these cables are actually routed through the roof space. Unlike most (All?) American services, none of this stuff is enclosed in conduit or raceway, so it wouldn't be very difficult for someone to tap the cables in his attic. Chances are that such a tap wouldn't be discovered for years.
I've never seen aything from the utilities about illegal taps being a big problem. Maybe they just rely on the fact that the majority of people would be too scared to interfere with hot 240V cables.
