@Dammit - Have you wired the earth and do you have an RCD in your consumer unit? It would be interesting to know if it has started tripping your consumer unit (assuming earth is wired and connected to the correct point in the lamp and that you have an RCD)
There was a lamp at my parents place that always gave a fairly strong "tingle" in operation. I dare say if it had an earth, the trip would have been going fairly constantly. My dad was adamant that all lamps lacked an earth connection. Maybe someone of the same school of thought?
My money would be on this.
@Dammit - Have you wired the earth and do you have an RCD in your consumer unit? It would be interesting to know if it has started tripping your consumer unit (assuming earth is wired and connected to the correct point in the lamp and that you have an RCD)