When the council electrician came today to re-wire the switch, he asked me which is source. I said I think it's at the bottom, that is, I thought power came up from the floorboards, thru the switch, then into the loft to the shower. But, it seems it's the opposite, source comes into the switch from the top. But, a simple test will indicate whether an error has been made. If the indicator is always on irrespective of the switch position, the wires need reversing. That's what I'm basically been told here. I'll have to get the council to correct the error. Thanks for the insight.