The energy company involved say that someone with the same name as me and a virtually identical email address had applied to switch. His messages had come to me. One of my current suppliers' call centre girls asked if she could pass me on to their IT/security department; they were very interested!
The particular address involved is one that I signed up to years ago and never used much. Just before Christmas I used it to order something online from a well-known retailer. Prior to that I had never received any messages in about 5 years and virtually no Spam. Since the New Year I've had about 30 messages and dozens of spam emails.
Advent laptop/Dell Inspiron 6000/Dell mini all using XP and 2Gb RAM
Dell Studio 15 with Win7 and 4Gb RAM
Belkin N router (cable) (VM 20Mb
Voyager 2100 via BT line (8Mb/s) as backup
BT Option 3 / Virgin cable 20Mbs
IE8 and OE6 (Live Mail with Win7)