I dont think it is a purely British Phenomenon.
Spam gets sent to the entire world. If it only worked on us Brits, then no spam would get sent anywhere but to Britain.
What the articles do not say is what % of spammed users respond in other countries.
We Brits may be the least likely to fall for it, or the most.
How many people reply to a junk mail letter offering a service/product, without looking into the company who sent it, or comparing the service/product with others?
Junk mail/spam in my flat gets binned, however good the offer looks. If i want something i will buy from who i choose, not from those who chose to target me. Perhaps i am in the minority with this approach though, as the spam and junk mail continue to be sent, in ever increasing amounts.