We have concerns about the increasing use of cheap/counterfeit phone chargers/plugs and the like on our sites and are looking to give people some advice about spotting the good from the bad. We have been told that one way to help spot a fake plug/charger is by looking for the BS and CE marking on them and that if they both appear on the plug/charger then it should raise concerns because it will probably be a fake. This, we are told, is because on a genuine plug/charger only one or other marking will appear, not both together. Do any of you good electrical people know if that is actually correct, it is not one have heard before?

What you've been told is incorrect. Appliances might carry any number of national approval marks along with the CE mark.
Better to focus on tightening up procurement and supply chains, and prohibiting use of personal chargers in the workplace. Failing that, you might consider a rule ensuring chargers aren't left unattended or switched on overnight.
This is a BIG problem, even authentic supply chains are at risk. Further background:

http://www.electricalsaf...y-unit/plug-in-chargers/
http://electrical.theiet...gs-chargers.cfm?type=pdf

News articles
http://www.bbc.co.uk/news/uk-27515446
http://www.bbc.co.uk/news/technology-24939681
http://www.bbc.co.uk/news/uk-27390466
http://www.bbc.co.uk/news/technology-27834310

It doesn't "stand" for Chinese Export. This was simply an ironic and humourous invention by some when discussing the tendency to outwardly copy (down to the exact detail) the authentic item.
The Counterfeiter new the item had to carry the mark, but he'd no idea what it meant.

Not just China, not just the Far East, and nothing new.
The Soviets impounded a B-29 bomber in 1944. It appeared later in production as the Tupolev 4.
The rudder pedals were copy-moulded and recast with the name "Boeing" still on them!