Long Life bulb

[beaky]

Is a PC processor high enough in the microwave spectrum to cause this?

Might be, but not enough wattage to do that, I think.
Cell phone, perhaps? It's a weird one.

I have a few of these in my room, and have never seen them flash when they're switched off.

If you have a voltmeter, luke, I'd be very curious to see if there's any actual current at that socket when the switch is off (with the bulb removed... don't try this if you don't know how, or you'll blow a fuse or breaker and maybe get zapped!)

[luke]

None of the above, the loft is over the ceiling and is nothing there.

I must check the cable wiring in the S/W & the bulb holder in case are reversed to L & N, as per power surge in the first answer I got from the mushroom department.

Thanks All anyway, see you and a Healthy New Year

[Chris_F]

A PC should be well shielded enough to not emit any significant RF (that's what all those FCC CE symbols on the side of the case mean).  If there's a high amp electrical line running close to the bulb (in the ceiling perhaps) that MAY do it, but it's unlikely.  For example, if your main house/appartment feed line went right near that bulb and somebody drew a ton of current on that line it could cause the bulb to give a faint glow.

My guess though would be something faulty in the electrical, just like you're investigating now.  My guess is that you're seeing a low voltage on the "hot" line when the switch is off when it should be entirely 0 voltage.  This may be a low enough voltage that a normal incandescent wouldn't light but the electronic balast on the compact flourescent is trying to strike the bulb by building up a charge then releasing.  This could be VERY bad in that it could overheat the ballast and cause a fire (a VERY LOW probability event though).  I recommend that you unscrew the bulb until you have it all sorted out.

[luke]

Sorry, too sientific for me, but somebody suggested a down to earth possible cause, reversed cables L & N in S/W & or bulb holder, which will try BUT after Xmas just in case the whole house flickers.....

But thank you all and will come back after trying Ritty's and all the other sugestions.

Have a good one now            luke

BTW
how do I get rid of this new thing popping up every time I post, asking to ".....include things from clipboard......." or something.