Laptop power costs....

I don't know if anybody else saw yesterdays Metro, but they had a story about costs to business of people plugging in their laptops in such as pubs and hotel reception areas and how much it was costing the businesses - they quoted a "survey" showing about 50p for a typical half hour period.
 
Pretty shocking, eh?
 
But let's think about it. On my bill, a unit of electricity is about 12p, and that's for a kW/h. So 50p should buy you around 4kW/h, yes?
 
Now, to consume 4kW/h in 30 minutes, your appliance must be consuming 8kW - equivalent to about 2-3 electric kettles, and about 32 amps. That wouldn't just blow the fuse on any 13 amp plug - it's a bit more than an entire normal 30 amp ring main could support!
 
Let's do the sums a different way. On the laptop I'm typing this on, the power supply is rated at 200 watts, though the actual consumption is probably a fair bit less, but let's use 200 watts as a ball park figure. So 0.2kW for 30 minutes would mean a total consumption of 0.1kW max, or about one tenth of a unit. In other words, the half hour usage is going to cost the pub/hotel more like 1p than 50p. (Probably a lot less, this is a large laptop.)
 
So where do these ridiculous stories come from, and just who has done the "survey" on which it's based? And how gullible are the reporters to just publish it without even a simple check of the facts? The danger is that we're now going to see various pubs etc banning allowing plugging in laptops for completely incorrect reasons - "I read it in the paper so it must be true".