I was told that when I wanted to send a few coins and tokens over (as you low value under £20) and just decided to risk it and send them, they arrived there safely about a week later. I got the impression it was just the post office covering themselves in case they did get destroyed
I agree with terrysoldpennies, it's an attempt at induced corrosion to mask the obvious differences normally evident in the repro 1933 pennies - the verdigris looks 'applied' especially on the obverse and if you study the kings head the differences seen on the repros are still evident. I've reported it.