I had this last year.We were on the approach to LGW inbound from POP on a nasty december morning.Without warning full power was applied and we made a go around.Once on the ground the Capt informed the crew that we were fully established on the ils and then all of a sudden it dissapeared ? The engineers checked the a/c and there was no problem and LGW said there was no problem with the ils.It later transpired that one of the crew at the rear of the a/c saw a pax turn on a mobile phone.This was the only explanation to what had happened.Some pax seem to think that we say turn off cd players and phones just to annoy them but things like this could have a tragic effect in the wrong place at the wrong time.