UK so talking 13amp. (30amp circuit)
Four way inline extension cable bought from Asda's today.
Plugged it in to power socket on wall switched on the extension inserted TV plug no problem, inserted top box plug as the 'live side went in about 1mm there was a blue flash. Never had this problem with any type of extension even with my old two outlet reel extension chopping and changing tools whilst extension reel 'live' Would the flash indicate a fault with that particular socket? I won't try it again as I've had my share of 'shocks' in the past, including waking up in the morning finding I'd got married heh! heh! and this one might be my last at 74.
Many thanks for reading and replies.

Bob, June 2015

this is common when plugging laptop power supplies etc. into live unswitched sockets.by slowly inserting plug you are causing an arc to jump between the live and load.turn off lead before connecting plugs,buy an extension with switched sockets or put plug in quickly.

geri j [electrician], January 2016

Thanks Phil,
a bad habbit yes but this is the first time I've experienced a flash from a socket attempting to insert a plug where in this incident the current jumped to the plug pin.
So its back to the store with the unit and see what they have to say.

bob, June 2015

I'm not an expert but if it was a small flash it's probably ok, just the electric sparking across the gap as it makes contact. Flashes you need to worry about are those that smell of burning or make a bang!
If you're concerned at all then take the lead back to the shop, explain that you think it's unsafe and ask them to swop it.
Time to change a habit of a lifetime and turn the mains off before plugging anything in!

Phil Price, June 2015