Exention cable?

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.