Flickering lamp

[johnf]

Strange but true. The overhead lamp in the hallway of my 1960's house flickers occasionally when someone walks underneath it. It's switched by two 2-way switches at either end of the hall, and my impression is that it happens more when one switch is used to switch the lamp off rather than the other. I've changed both switches, the lampholder (plastic), flex (2-core), and ceiling rose. Vibration? The floor is concrete. Air disturbance? The shade is heavy glass. The lamp seems to last as long as others in the house, and is in use every night. When I have needed to change it, the new bulb flickers when I put it in, though I can't detect any current in the lampholder with a mains-tester screwdriver.
Any ideas, please?

 

[securespark]

There has to be a dicky connection somewhere for it to flicker. Movement is causing a poor connection to move.

Remove the light fitting a replace with a temporary lampholder you know is OK.

What happens?

 

[johnf]

OK, thanks I'll give that a try at the weekend. I should clarify that the flickering occurs when the light is OFF, not (as far as I've noticed) when it's on. Don't know if that makes any difference...

 

[securespark]

Have you changed the switch?

 

[breezer]

Have you changed the switch?

does this bit answer that?

I've changed both switches,

 

[securespark]

Oh, Breezer, you don't miss a trick!

OK, hands up.......

In that case, it sounds like it COULD be live loop & switched live shorting?