The name is German, but as I live in England my last name is never spelt correctly - I will always
get PetersOn. People have previously not been able to find me on computer lists (e.g. at the travel agents) because they had
misspelt my surname. I try telling them that it's "Petersen, with all e's", but that usually confuses them to the extent that
they make me spell it all out.

I am surprised that you have such trouble! Here in Portland, Oregon, USA, there are 1 1/2 pages of Petersens, and 3 pages of Petersons in the phone directory. Thus, your spelling, while half as common, is far from rare. I had been told that the "en" version was Norwegian in origin, whereas the "on" version was Swedish. Am I misinformed?